Merge

make/java/java/FILES_java.gmk

@@ -286,11 +286,18 @@ JAVA_JAVA_java = \
     java/util/concurrent/ExecutorService.java \
     java/util/concurrent/ExecutorCompletionService.java \
     java/util/concurrent/Executors.java \
+    java/util/concurrent/ForkJoinPool.java \
+    java/util/concurrent/ForkJoinTask.java \
+    java/util/concurrent/ForkJoinWorkerThread.java \
     java/util/concurrent/Future.java \
     java/util/concurrent/FutureTask.java \
     java/util/concurrent/LinkedBlockingDeque.java \
     java/util/concurrent/LinkedBlockingQueue.java \
+    java/util/concurrent/LinkedTransferQueue.java \
+    java/util/concurrent/Phaser.java \
     java/util/concurrent/PriorityBlockingQueue.java \
+    java/util/concurrent/RecursiveAction.java \
+    java/util/concurrent/RecursiveTask.java \
     java/util/concurrent/RejectedExecutionException.java \
     java/util/concurrent/RejectedExecutionHandler.java \
     java/util/concurrent/RunnableFuture.java \
@@ -301,9 +308,11 @@ JAVA_JAVA_java = \
     java/util/concurrent/Semaphore.java \
     java/util/concurrent/SynchronousQueue.java \
     java/util/concurrent/ThreadFactory.java \
+    java/util/concurrent/ThreadLocalRandom.java \
     java/util/concurrent/ThreadPoolExecutor.java \
     java/util/concurrent/TimeUnit.java \
     java/util/concurrent/TimeoutException.java \
+    java/util/concurrent/TransferQueue.java \
     java/util/concurrent/atomic/AtomicBoolean.java \
     java/util/concurrent/atomic/AtomicInteger.java \
     java/util/concurrent/atomic/AtomicIntegerArray.java \

src/share/classes/java/util/AbstractList.java

@@ -256,9 +256,8 @@ public abstract class AbstractList<E> extends AbstractCollection<E> implements L
     public boolean addAll(int index, Collection<? extends E> c) {
         rangeCheckForAdd(index);
         boolean modified = false;
-        Iterator<? extends E> e = c.iterator();
-        while (e.hasNext()) {
-            add(index++, e.next());
+        for (E e : c) {
+            add(index++, e);
             modified = true;
         }
         return modified;

src/share/classes/java/util/AbstractQueue.java

@@ -183,11 +183,9 @@ public abstract class AbstractQueue<E>
         if (c == this)
             throw new IllegalArgumentException();
         boolean modified = false;
-        Iterator<? extends E> e = c.iterator();
-        while (e.hasNext()) {
-            if (add(e.next()))
+        for (E e : c)
+            if (add(e))
                 modified = true;
-        }
         return modified;
     }
 

src/share/classes/java/util/HashMap.java

@@ -448,11 +448,9 @@ public class HashMap<K,V>
     }
 
     private void putAllForCreate(Map<? extends K, ? extends V> m) {
-        for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
-            Map.Entry<? extends K, ? extends V> e = i.next();
+        for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
             putForCreate(e.getKey(), e.getValue());
     }
-    }
 
     /**
      * Rehashes the contents of this map into a new array with a
@@ -536,11 +534,9 @@ public class HashMap<K,V>
                 resize(newCapacity);
         }
 
-        for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m.entrySet().iterator(); i.hasNext(); ) {
-            Map.Entry<? extends K, ? extends V> e = i.next();
+        for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
             put(e.getKey(), e.getValue());
     }
-    }
 
     /**
      * Removes the mapping for the specified key from this map if present.

src/share/classes/java/util/HashSet.java

@@ -280,8 +280,8 @@ public class HashSet<E>
         s.writeInt(map.size());
 
         // Write out all elements in the proper order.
-        for (Iterator i=map.keySet().iterator(); i.hasNext(); )
-            s.writeObject(i.next());
+        for (E e : map.keySet())
+            s.writeObject(e);
     }
 
     /**

src/share/classes/java/util/Random.java

@@ -50,6 +50,18 @@ import sun.misc.Unsafe;
  * <p>
  * Many applications will find the method {@link Math#random} simpler to use.
  *
+ * <p>Instances of {@code java.util.Random} are threadsafe.
+ * However, the concurrent use of the same {@code java.util.Random}
+ * instance across threads may encounter contention and consequent
+ * poor performance. Consider instead using
+ * {@link java.util.concurrent.ThreadLocalRandom} in multithreaded
+ * designs.
+ *
+ * <p>Instances of {@code java.util.Random} are not cryptographically
+ * secure.  Consider instead using {@link java.security.SecureRandom} to
+ * get a cryptographically secure pseudo-random number generator for use
+ * by security-sensitive applications.
+ *
  * @author  Frank Yellin
  * @since   1.0
  */

src/share/classes/java/util/concurrent/ArrayBlockingQueue.java

@@ -218,8 +218,8 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
         if (capacity < c.size())
             throw new IllegalArgumentException();
 
-        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
-            add(it.next());
+        for (E e : c)
+            add(e);
     }
 
     /**

src/share/classes/java/util/concurrent/ConcurrentLinkedQueue.java

@@ -250,8 +250,8 @@ public class ConcurrentLinkedQueue<E> extends AbstractQueue<E>
      *         of its elements are null
      */
     public ConcurrentLinkedQueue(Collection<? extends E> c) {
-        for (Iterator<? extends E> it = c.iterator(); it.hasNext();)
-            add(it.next());
+        for (E e : c)
+            add(e);
     }
 
     // Have to override just to update the javadoc

src/share/classes/java/util/concurrent/ConcurrentSkipListMap.java

@@ -895,7 +895,7 @@ public class ConcurrentSkipListMap<K,V> extends AbstractMap<K,V>
                 if (n != null) {
                     Node<K,V> f = n.next;
                     if (n != b.next)               // inconsistent read
-                        break;;
+                        break;
                     Object v = n.value;
                     if (v == null) {               // n is deleted
                         n.helpDelete(b, f);

src/share/classes/java/util/concurrent/CountDownLatch.java

@@ -148,7 +148,8 @@ import java.util.concurrent.atomic.*;
  *
  * </pre>
  *
- * <p>Memory consistency effects: Actions in a thread prior to calling
+ * <p>Memory consistency effects: Until the count reaches
+ * zero, actions in a thread prior to calling
  * {@code countDown()}
  * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
  * actions following a successful return from a corresponding

src/share/classes/java/util/concurrent/ExecutorService.java

@@ -332,8 +332,8 @@ public interface ExecutorService extends Executor {
      * @param tasks the collection of tasks
      * @return the result returned by one of the tasks
      * @throws InterruptedException if interrupted while waiting
-     * @throws NullPointerException if tasks or any of its elements
-     *         are <tt>null</tt>
+     * @throws NullPointerException if tasks or any element task
+     *         subject to execution is <tt>null</tt>
      * @throws IllegalArgumentException if tasks is empty
      * @throws ExecutionException if no task successfully completes
      * @throws RejectedExecutionException if tasks cannot be scheduled
@@ -356,8 +356,8 @@ public interface ExecutorService extends Executor {
      * @param unit the time unit of the timeout argument
      * @return the result returned by one of the tasks.
      * @throws InterruptedException if interrupted while waiting
-     * @throws NullPointerException if tasks, any of its elements, or
-     *         unit are <tt>null</tt>
+     * @throws NullPointerException if tasks, or unit, or any element
+     *         task subject to execution is <tt>null</tt>
      * @throws TimeoutException if the given timeout elapses before
      *         any task successfully completes
      * @throws ExecutionException if no task successfully completes

src/share/classes/java/util/concurrent/ForkJoinPool.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.LockSupport;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * An {@link ExecutorService} for running {@link ForkJoinTask}s.
+ * A {@code ForkJoinPool} provides the entry point for submissions
+ * from non-{@code ForkJoinTask}s, as well as management and
+ * monitoring operations.
+ *
+ * <p>A {@code ForkJoinPool} differs from other kinds of {@link
+ * ExecutorService} mainly by virtue of employing
+ * <em>work-stealing</em>: all threads in the pool attempt to find and
+ * execute subtasks created by other active tasks (eventually blocking
+ * waiting for work if none exist). This enables efficient processing
+ * when most tasks spawn other subtasks (as do most {@code
+ * ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
+ * execution of some plain {@code Runnable}- or {@code Callable}-
+ * based activities along with {@code ForkJoinTask}s. When setting
+ * {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
+ * also be appropriate for use with fine-grained tasks of any form
+ * that are never joined. Otherwise, other {@code ExecutorService}
+ * implementations are typically more appropriate choices.
+ *
+ * <p>A {@code ForkJoinPool} is constructed with a given target
+ * parallelism level; by default, equal to the number of available
+ * processors. Unless configured otherwise via {@link
+ * #setMaintainsParallelism}, the pool attempts to maintain this
+ * number of active (or available) threads by dynamically adding,
+ * suspending, or resuming internal worker threads, even if some tasks
+ * are stalled waiting to join others. However, no such adjustments
+ * are performed in the face of blocked IO or other unmanaged
+ * synchronization. The nested {@link ManagedBlocker} interface
+ * enables extension of the kinds of synchronization accommodated.
+ * The target parallelism level may also be changed dynamically
+ * ({@link #setParallelism}). The total number of threads may be
+ * limited using method {@link #setMaximumPoolSize}, in which case it
+ * may become possible for the activities of a pool to stall due to
+ * the lack of available threads to process new tasks.
+ *
+ * <p>In addition to execution and lifecycle control methods, this
+ * class provides status check methods (for example
+ * {@link #getStealCount}) that are intended to aid in developing,
+ * tuning, and monitoring fork/join applications. Also, method
+ * {@link #toString} returns indications of pool state in a
+ * convenient form for informal monitoring.
+ *
+ * <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
+ * used for all parallel task execution in a program or subsystem.
+ * Otherwise, use would not usually outweigh the construction and
+ * bookkeeping overhead of creating a large set of threads. For
+ * example, a common pool could be used for the {@code SortTasks}
+ * illustrated in {@link RecursiveAction}. Because {@code
+ * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
+ * daemon} mode, there is typically no need to explicitly {@link
+ * #shutdown} such a pool upon program exit.
+ *
+ * <pre>
+ * static final ForkJoinPool mainPool = new ForkJoinPool();
+ * ...
+ * public void sort(long[] array) {
+ *   mainPool.invoke(new SortTask(array, 0, array.length));
+ * }
+ * </pre>
+ *
+ * <p><b>Implementation notes</b>: This implementation restricts the
+ * maximum number of running threads to 32767. Attempts to create
+ * pools with greater than the maximum number result in
+ * {@code IllegalArgumentException}.
+ *
+ * <p>This implementation rejects submitted tasks (that is, by throwing
+ * {@link RejectedExecutionException}) only when the pool is shut down.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ForkJoinPool extends AbstractExecutorService {
+
+    /*
+     * See the extended comments interspersed below for design,
+     * rationale, and walkthroughs.
+     */
+
+    /** Mask for packing and unpacking shorts */
+    private static final int  shortMask = 0xffff;
+
+    /** Max pool size -- must be a power of two minus 1 */
+    private static final int MAX_THREADS =  0x7FFF;
+
+    /**
+     * Factory for creating new {@link ForkJoinWorkerThread}s.
+     * A {@code ForkJoinWorkerThreadFactory} must be defined and used
+     * for {@code ForkJoinWorkerThread} subclasses that extend base
+     * functionality or initialize threads with different contexts.
+     */
+    public static interface ForkJoinWorkerThreadFactory {
+        /**
+         * Returns a new worker thread operating in the given pool.
+         *
+         * @param pool the pool this thread works in
+         * @throws NullPointerException if the pool is null
+         */
+        public ForkJoinWorkerThread newThread(ForkJoinPool pool);
+    }
+
+    /**
+     * Default ForkJoinWorkerThreadFactory implementation; creates a
+     * new ForkJoinWorkerThread.
+     */
+    static class  DefaultForkJoinWorkerThreadFactory
+        implements ForkJoinWorkerThreadFactory {
+        public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
+            try {
+                return new ForkJoinWorkerThread(pool);
+            } catch (OutOfMemoryError oom)  {
+                return null;
+            }
+        }
+    }
+
+    /**
+     * Creates a new ForkJoinWorkerThread. This factory is used unless
+     * overridden in ForkJoinPool constructors.
+     */
+    public static final ForkJoinWorkerThreadFactory
+        defaultForkJoinWorkerThreadFactory =
+        new DefaultForkJoinWorkerThreadFactory();
+
+    /**
+     * Permission required for callers of methods that may start or
+     * kill threads.
+     */
+    private static final RuntimePermission modifyThreadPermission =
+        new RuntimePermission("modifyThread");
+
+    /**
+     * If there is a security manager, makes sure caller has
+     * permission to modify threads.
+     */
+    private static void checkPermission() {
+        SecurityManager security = System.getSecurityManager();
+        if (security != null)
+            security.checkPermission(modifyThreadPermission);
+    }
+
+    /**
+     * Generator for assigning sequence numbers as pool names.
+     */
+    private static final AtomicInteger poolNumberGenerator =
+        new AtomicInteger();
+
+    /**
+     * Array holding all worker threads in the pool. Initialized upon
+     * first use. Array size must be a power of two.  Updates and
+     * replacements are protected by workerLock, but it is always kept
+     * in a consistent enough state to be randomly accessed without
+     * locking by workers performing work-stealing.
+     */
+    volatile ForkJoinWorkerThread[] workers;
+
+    /**
+     * Lock protecting access to workers.
+     */
+    private final ReentrantLock workerLock;
+
+    /**
+     * Condition for awaitTermination.
+     */
+    private final Condition termination;
+
+    /**
+     * The uncaught exception handler used when any worker
+     * abruptly terminates
+     */
+    private Thread.UncaughtExceptionHandler ueh;
+
+    /**
+     * Creation factory for worker threads.
+     */
+    private final ForkJoinWorkerThreadFactory factory;
+
+    /**
+     * Head of stack of threads that were created to maintain
+     * parallelism when other threads blocked, but have since
+     * suspended when the parallelism level rose.
+     */
+    private volatile WaitQueueNode spareStack;
+
+    /**
+     * Sum of per-thread steal counts, updated only when threads are
+     * idle or terminating.
+     */
+    private final AtomicLong stealCount;
+
+    /**
+     * Queue for external submissions.
+     */
+    private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
+
+    /**
+     * Head of Treiber stack for barrier sync. See below for explanation.
+     */
+    private volatile WaitQueueNode syncStack;
+
+    /**
+     * The count for event barrier
+     */
+    private volatile long eventCount;
+
+    /**
+     * Pool number, just for assigning useful names to worker threads
+     */
+    private final int poolNumber;
+
+    /**
+     * The maximum allowed pool size
+     */
+    private volatile int maxPoolSize;
+
+    /**
+     * The desired parallelism level, updated only under workerLock.
+     */
+    private volatile int parallelism;
+
+    /**
+     * True if use local fifo, not default lifo, for local polling
+     */
+    private volatile boolean locallyFifo;
+
+    /**
+     * Holds number of total (i.e., created and not yet terminated)
+     * and running (i.e., not blocked on joins or other managed sync)
+     * threads, packed into one int to ensure consistent snapshot when
+     * making decisions about creating and suspending spare
+     * threads. Updated only by CAS.  Note: CASes in
+     * updateRunningCount and preJoin assume that running active count
+     * is in low word, so need to be modified if this changes.
+     */
+    private volatile int workerCounts;
+
+    private static int totalCountOf(int s)           { return s >>> 16;  }
+    private static int runningCountOf(int s)         { return s & shortMask; }
+    private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
+
+    /**
+     * Adds delta (which may be negative) to running count.  This must
+     * be called before (with negative arg) and after (with positive)
+     * any managed synchronization (i.e., mainly, joins).
+     *
+     * @param delta the number to add
+     */
+    final void updateRunningCount(int delta) {
+        int s;
+        do {} while (!casWorkerCounts(s = workerCounts, s + delta));
+    }
+
+    /**
+     * Adds delta (which may be negative) to both total and running
+     * count.  This must be called upon creation and termination of
+     * worker threads.
+     *
+     * @param delta the number to add
+     */
+    private void updateWorkerCount(int delta) {
+        int d = delta + (delta << 16); // add to both lo and hi parts
+        int s;
+        do {} while (!casWorkerCounts(s = workerCounts, s + d));
+    }
+
+    /**
+     * Lifecycle control. High word contains runState, low word
+     * contains the number of workers that are (probably) executing
+     * tasks. This value is atomically incremented before a worker
+     * gets a task to run, and decremented when worker has no tasks
+     * and cannot find any. These two fields are bundled together to
+     * support correct termination triggering.  Note: activeCount
+     * CAS'es cheat by assuming active count is in low word, so need
+     * to be modified if this changes
+     */
+    private volatile int runControl;
+
+    // RunState values. Order among values matters
+    private static final int RUNNING     = 0;
+    private static final int SHUTDOWN    = 1;
+    private static final int TERMINATING = 2;
+    private static final int TERMINATED  = 3;
+
+    private static int runStateOf(int c)             { return c >>> 16; }
+    private static int activeCountOf(int c)          { return c & shortMask; }
+    private static int runControlFor(int r, int a)   { return (r << 16) + a; }
+
+    /**
+     * Tries incrementing active count; fails on contention.
+     * Called by workers before/during executing tasks.
+     *
+     * @return true on success
+     */
+    final boolean tryIncrementActiveCount() {
+        int c = runControl;
+        return casRunControl(c, c+1);
+    }
+
+    /**
+     * Tries decrementing active count; fails on contention.
+     * Possibly triggers termination on success.
+     * Called by workers when they can't find tasks.
+     *
+     * @return true on success
+     */
+    final boolean tryDecrementActiveCount() {
+        int c = runControl;
+        int nextc = c - 1;
+        if (!casRunControl(c, nextc))
+            return false;
+        if (canTerminateOnShutdown(nextc))
+            terminateOnShutdown();
+        return true;
+    }
+
+    /**
+     * Returns {@code true} if argument represents zero active count
+     * and nonzero runstate, which is the triggering condition for
+     * terminating on shutdown.
+     */
+    private static boolean canTerminateOnShutdown(int c) {
+        // i.e. least bit is nonzero runState bit
+        return ((c & -c) >>> 16) != 0;
+    }
+
+    /**
+     * Transition run state to at least the given state. Return true
+     * if not already at least given state.
+     */
+    private boolean transitionRunStateTo(int state) {
+        for (;;) {
+            int c = runControl;
+            if (runStateOf(c) >= state)
+                return false;
+            if (casRunControl(c, runControlFor(state, activeCountOf(c))))
+                return true;
+        }
+    }
+
+    /**
+     * Controls whether to add spares to maintain parallelism
+     */
+    private volatile boolean maintainsParallelism;
+
+    // Constructors
+
+    /**
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+     * java.lang.Runtime#availableProcessors}, and using the {@linkplain
+     * #defaultForkJoinWorkerThreadFactory default thread factory}.
+     *
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public ForkJoinPool() {
+        this(Runtime.getRuntime().availableProcessors(),
+             defaultForkJoinWorkerThreadFactory);
+    }
+
+    /**
+     * Creates a {@code ForkJoinPool} with the indicated parallelism
+     * level and using the {@linkplain
+     * #defaultForkJoinWorkerThreadFactory default thread factory}.
+     *
+     * @param parallelism the parallelism level
+     * @throws IllegalArgumentException if parallelism less than or
+     *         equal to zero, or greater than implementation limit
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public ForkJoinPool(int parallelism) {
+        this(parallelism, defaultForkJoinWorkerThreadFactory);
+    }
+
+    /**
+     * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+     * java.lang.Runtime#availableProcessors}, and using the given
+     * thread factory.
+     *
+     * @param factory the factory for creating new threads
+     * @throws NullPointerException if the factory is null
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
+        this(Runtime.getRuntime().availableProcessors(), factory);
+    }
+
+    /**
+     * Creates a {@code ForkJoinPool} with the given parallelism and
+     * thread factory.
+     *
+     * @param parallelism the parallelism level
+     * @param factory the factory for creating new threads
+     * @throws IllegalArgumentException if parallelism less than or
+     *         equal to zero, or greater than implementation limit
+     * @throws NullPointerException if the factory is null
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
+        if (parallelism <= 0 || parallelism > MAX_THREADS)
+            throw new IllegalArgumentException();
+        if (factory == null)
+            throw new NullPointerException();
+        checkPermission();
+        this.factory = factory;
+        this.parallelism = parallelism;
+        this.maxPoolSize = MAX_THREADS;
+        this.maintainsParallelism = true;
+        this.poolNumber = poolNumberGenerator.incrementAndGet();
+        this.workerLock = new ReentrantLock();
+        this.termination = workerLock.newCondition();
+        this.stealCount = new AtomicLong();
+        this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
+        // worker array and workers are lazily constructed
+    }
+
+    /**
+     * Creates a new worker thread using factory.
+     *
+     * @param index the index to assign worker
+     * @return new worker, or null if factory failed
+     */
+    private ForkJoinWorkerThread createWorker(int index) {
+        Thread.UncaughtExceptionHandler h = ueh;
+        ForkJoinWorkerThread w = factory.newThread(this);
+        if (w != null) {
+            w.poolIndex = index;
+            w.setDaemon(true);
+            w.setAsyncMode(locallyFifo);
+            w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
+            if (h != null)
+                w.setUncaughtExceptionHandler(h);
+        }
+        return w;
+    }
+
+    /**
+     * Returns a good size for worker array given pool size.
+     * Currently requires size to be a power of two.
+     */
+    private static int arraySizeFor(int poolSize) {
+        if (poolSize <= 1)
+            return 1;
+        // See Hackers Delight, sec 3.2
+        int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
+        c |= c >>>  1;
+        c |= c >>>  2;
+        c |= c >>>  4;
+        c |= c >>>  8;
+        c |= c >>> 16;
+        return c + 1;
+    }
+
+    /**
+     * Creates or resizes array if necessary to hold newLength.
+     * Call only under exclusion.
+     *
+     * @return the array
+     */
+    private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws == null)
+            return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
+        else if (newLength > ws.length)
+            return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
+        else
+            return ws;
+    }
+
+    /**
+     * Tries to shrink workers into smaller array after one or more terminate.
+     */
+    private void tryShrinkWorkerArray() {
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws != null) {
+            int len = ws.length;
+            int last = len - 1;
+            while (last >= 0 && ws[last] == null)
+                --last;
+            int newLength = arraySizeFor(last+1);
+            if (newLength < len)
+                workers = Arrays.copyOf(ws, newLength);
+        }
+    }
+
+    /**
+     * Initializes workers if necessary.
+     */
+    final void ensureWorkerInitialization() {
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws == null) {
+            final ReentrantLock lock = this.workerLock;
+            lock.lock();
+            try {
+                ws = workers;
+                if (ws == null) {
+                    int ps = parallelism;
+                    ws = ensureWorkerArrayCapacity(ps);
+                    for (int i = 0; i < ps; ++i) {
+                        ForkJoinWorkerThread w = createWorker(i);
+                        if (w != null) {
+                            ws[i] = w;
+                            w.start();
+                            updateWorkerCount(1);
+                        }
+                    }
+                }
+            } finally {
+                lock.unlock();
+            }
+        }
+    }
+
+    /**
+     * Worker creation and startup for threads added via setParallelism.
+     */
+    private void createAndStartAddedWorkers() {
+        resumeAllSpares();  // Allow spares to convert to nonspare
+        int ps = parallelism;
+        ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
+        int len = ws.length;
+        // Sweep through slots, to keep lowest indices most populated
+        int k = 0;
+        while (k < len) {
+            if (ws[k] != null) {
+                ++k;
+                continue;
+            }
+            int s = workerCounts;
+            int tc = totalCountOf(s);
+            int rc = runningCountOf(s);
+            if (rc >= ps || tc >= ps)
+                break;
+            if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
+                ForkJoinWorkerThread w = createWorker(k);
+                if (w != null) {
+                    ws[k++] = w;
+                    w.start();
+                }
+                else {
+                    updateWorkerCount(-1); // back out on failed creation
+                    break;
+                }
+            }
+        }
+    }
+
+    // Execution methods
+
+    /**
+     * Common code for execute, invoke and submit
+     */
+    private <T> void doSubmit(ForkJoinTask<T> task) {
+        if (task == null)
+            throw new NullPointerException();
+        if (isShutdown())
+            throw new RejectedExecutionException();
+        if (workers == null)
+            ensureWorkerInitialization();
+        submissionQueue.offer(task);
+        signalIdleWorkers();
+    }
+
+    /**
+     * Performs the given task, returning its result upon completion.
+     *
+     * @param task the task
+     * @return the task's result
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public <T> T invoke(ForkJoinTask<T> task) {
+        doSubmit(task);
+        return task.join();
+    }
+
+    /**
+     * Arranges for (asynchronous) execution of the given task.
+     *
+     * @param task the task
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public void execute(ForkJoinTask<?> task) {
+        doSubmit(task);
+    }
+
+    // AbstractExecutorService methods
+
+    /**
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public void execute(Runnable task) {
+        ForkJoinTask<?> job;
+        if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+            job = (ForkJoinTask<?>) task;
+        else
+            job = ForkJoinTask.adapt(task, null);
+        doSubmit(job);
+    }
+
+    /**
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public <T> ForkJoinTask<T> submit(Callable<T> task) {
+        ForkJoinTask<T> job = ForkJoinTask.adapt(task);
+        doSubmit(job);
+        return job;
+    }
+
+    /**
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public <T> ForkJoinTask<T> submit(Runnable task, T result) {
+        ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
+        doSubmit(job);
+        return job;
+    }
+
+    /**
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public ForkJoinTask<?> submit(Runnable task) {
+        ForkJoinTask<?> job;
+        if (task instanceof ForkJoinTask<?>) // avoid re-wrap
+            job = (ForkJoinTask<?>) task;
+        else
+            job = ForkJoinTask.adapt(task, null);
+        doSubmit(job);
+        return job;
+    }
+
+    /**
+     * Submits a ForkJoinTask for execution.
+     *
+     * @param task the task to submit
+     * @return the task
+     * @throws NullPointerException if the task is null
+     * @throws RejectedExecutionException if the task cannot be
+     *         scheduled for execution
+     */
+    public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
+        doSubmit(task);
+        return task;
+    }
+
+
+    /**
+     * @throws NullPointerException       {@inheritDoc}
+     * @throws RejectedExecutionException {@inheritDoc}
+     */
+    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
+        ArrayList<ForkJoinTask<T>> forkJoinTasks =
+            new ArrayList<ForkJoinTask<T>>(tasks.size());
+        for (Callable<T> task : tasks)
+            forkJoinTasks.add(ForkJoinTask.adapt(task));
+        invoke(new InvokeAll<T>(forkJoinTasks));
+
+        @SuppressWarnings({"unchecked", "rawtypes"})
+        List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
+        return futures;
+    }
+
+    static final class InvokeAll<T> extends RecursiveAction {
+        final ArrayList<ForkJoinTask<T>> tasks;
+        InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
+        public void compute() {
+            try { invokeAll(tasks); }
+            catch (Exception ignore) {}
+        }
+        private static final long serialVersionUID = -7914297376763021607L;
+    }
+
+    // Configuration and status settings and queries
+
+    /**
+     * Returns the factory used for constructing new workers.
+     *
+     * @return the factory used for constructing new workers
+     */
+    public ForkJoinWorkerThreadFactory getFactory() {
+        return factory;
+    }
+
+    /**
+     * Returns the handler for internal worker threads that terminate
+     * due to unrecoverable errors encountered while executing tasks.
+     *
+     * @return the handler, or {@code null} if none
+     */
+    public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
+        Thread.UncaughtExceptionHandler h;
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            h = ueh;
+        } finally {
+            lock.unlock();
+        }
+        return h;
+    }
+
+    /**
+     * Sets the handler for internal worker threads that terminate due
+     * to unrecoverable errors encountered while executing tasks.
+     * Unless set, the current default or ThreadGroup handler is used
+     * as handler.
+     *
+     * @param h the new handler
+     * @return the old handler, or {@code null} if none
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public Thread.UncaughtExceptionHandler
+        setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
+        checkPermission();
+        Thread.UncaughtExceptionHandler old = null;
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            old = ueh;
+            ueh = h;
+            ForkJoinWorkerThread[] ws = workers;
+            if (ws != null) {
+                for (int i = 0; i < ws.length; ++i) {
+                    ForkJoinWorkerThread w = ws[i];
+                    if (w != null)
+                        w.setUncaughtExceptionHandler(h);
+                }
+            }
+        } finally {
+            lock.unlock();
+        }
+        return old;
+    }
+
+
+    /**
+     * Sets the target parallelism level of this pool.
+     *
+     * @param parallelism the target parallelism
+     * @throws IllegalArgumentException if parallelism less than or
+     * equal to zero or greater than maximum size bounds
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public void setParallelism(int parallelism) {
+        checkPermission();
+        if (parallelism <= 0 || parallelism > maxPoolSize)
+            throw new IllegalArgumentException();
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            if (isProcessingTasks()) {
+                int p = this.parallelism;
+                this.parallelism = parallelism;
+                if (parallelism > p)
+                    createAndStartAddedWorkers();
+                else
+                    trimSpares();
+            }
+        } finally {
+            lock.unlock();
+        }
+        signalIdleWorkers();
+    }
+
+    /**
+     * Returns the targeted parallelism level of this pool.
+     *
+     * @return the targeted parallelism level of this pool
+     */
+    public int getParallelism() {
+        return parallelism;
+    }
+
+    /**
+     * Returns the number of worker threads that have started but not
+     * yet terminated.  This result returned by this method may differ
+     * from {@link #getParallelism} when threads are created to
+     * maintain parallelism when others are cooperatively blocked.
+     *
+     * @return the number of worker threads
+     */
+    public int getPoolSize() {
+        return totalCountOf(workerCounts);
+    }
+
+    /**
+     * Returns the maximum number of threads allowed to exist in the
+     * pool. Unless set using {@link #setMaximumPoolSize}, the
+     * maximum is an implementation-defined value designed only to
+     * prevent runaway growth.
+     *
+     * @return the maximum
+     */
+    public int getMaximumPoolSize() {
+        return maxPoolSize;
+    }
+
+    /**
+     * Sets the maximum number of threads allowed to exist in the
+     * pool. The given value should normally be greater than or equal
+     * to the {@link #getParallelism parallelism} level. Setting this
+     * value has no effect on current pool size. It controls
+     * construction of new threads.
+     *
+     * @throws IllegalArgumentException if negative or greater than
+     * internal implementation limit
+     */
+    public void setMaximumPoolSize(int newMax) {
+        if (newMax < 0 || newMax > MAX_THREADS)
+            throw new IllegalArgumentException();
+        maxPoolSize = newMax;
+    }
+
+
+    /**
+     * Returns {@code true} if this pool dynamically maintains its
+     * target parallelism level. If false, new threads are added only
+     * to avoid possible starvation.  This setting is by default true.
+     *
+     * @return {@code true} if maintains parallelism
+     */
+    public boolean getMaintainsParallelism() {
+        return maintainsParallelism;
+    }
+
+    /**
+     * Sets whether this pool dynamically maintains its target
+     * parallelism level. If false, new threads are added only to
+     * avoid possible starvation.
+     *
+     * @param enable {@code true} to maintain parallelism
+     */
+    public void setMaintainsParallelism(boolean enable) {
+        maintainsParallelism = enable;
+    }
+
+    /**
+     * Establishes local first-in-first-out scheduling mode for forked
+     * tasks that are never joined. This mode may be more appropriate
+     * than default locally stack-based mode in applications in which
+     * worker threads only process asynchronous tasks.  This method is
+     * designed to be invoked only when the pool is quiescent, and
+     * typically only before any tasks are submitted. The effects of
+     * invocations at other times may be unpredictable.
+     *
+     * @param async if {@code true}, use locally FIFO scheduling
+     * @return the previous mode
+     * @see #getAsyncMode
+     */
+    public boolean setAsyncMode(boolean async) {
+        boolean oldMode = locallyFifo;
+        locallyFifo = async;
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws != null) {
+            for (int i = 0; i < ws.length; ++i) {
+                ForkJoinWorkerThread t = ws[i];
+                if (t != null)
+                    t.setAsyncMode(async);
+            }
+        }
+        return oldMode;
+    }
+
+    /**
+     * Returns {@code true} if this pool uses local first-in-first-out
+     * scheduling mode for forked tasks that are never joined.
+     *
+     * @return {@code true} if this pool uses async mode
+     * @see #setAsyncMode
+     */
+    public boolean getAsyncMode() {
+        return locallyFifo;
+    }
+
+    /**
+     * Returns an estimate of the number of worker threads that are
+     * not blocked waiting to join tasks or for other managed
+     * synchronization.
+     *
+     * @return the number of worker threads
+     */
+    public int getRunningThreadCount() {
+        return runningCountOf(workerCounts);
+    }
+
+    /**
+     * Returns an estimate of the number of threads that are currently
+     * stealing or executing tasks. This method may overestimate the
+     * number of active threads.
+     *
+     * @return the number of active threads
+     */
+    public int getActiveThreadCount() {
+        return activeCountOf(runControl);
+    }
+
+    /**
+     * Returns an estimate of the number of threads that are currently
+     * idle waiting for tasks. This method may underestimate the
+     * number of idle threads.
+     *
+     * @return the number of idle threads
+     */
+    final int getIdleThreadCount() {
+        int c = runningCountOf(workerCounts) - activeCountOf(runControl);
+        return (c <= 0) ? 0 : c;
+    }
+
+    /**
+     * Returns {@code true} if all worker threads are currently idle.
+     * An idle worker is one that cannot obtain a task to execute
+     * because none are available to steal from other threads, and
+     * there are no pending submissions to the pool. This method is
+     * conservative; it might not return {@code true} immediately upon
+     * idleness of all threads, but will eventually become true if
+     * threads remain inactive.
+     *
+     * @return {@code true} if all threads are currently idle
+     */
+    public boolean isQuiescent() {
+        return activeCountOf(runControl) == 0;
+    }
+
+    /**
+     * Returns an estimate of the total number of tasks stolen from
+     * one thread's work queue by another. The reported value
+     * underestimates the actual total number of steals when the pool
+     * is not quiescent. This value may be useful for monitoring and
+     * tuning fork/join programs: in general, steal counts should be
+     * high enough to keep threads busy, but low enough to avoid
+     * overhead and contention across threads.
+     *
+     * @return the number of steals
+     */
+    public long getStealCount() {
+        return stealCount.get();
+    }
+
+    /**
+     * Accumulates steal count from a worker.
+     * Call only when worker known to be idle.
+     */
+    private void updateStealCount(ForkJoinWorkerThread w) {
+        int sc = w.getAndClearStealCount();
+        if (sc != 0)
+            stealCount.addAndGet(sc);
+    }
+
+    /**
+     * Returns an estimate of the total number of tasks currently held
+     * in queues by worker threads (but not including tasks submitted
+     * to the pool that have not begun executing). This value is only
+     * an approximation, obtained by iterating across all threads in
+     * the pool. This method may be useful for tuning task
+     * granularities.
+     *
+     * @return the number of queued tasks
+     */
+    public long getQueuedTaskCount() {
+        long count = 0;
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws != null) {
+            for (int i = 0; i < ws.length; ++i) {
+                ForkJoinWorkerThread t = ws[i];
+                if (t != null)
+                    count += t.getQueueSize();
+            }
+        }
+        return count;
+    }
+
+    /**
+     * Returns an estimate of the number of tasks submitted to this
+     * pool that have not yet begun executing.  This method takes time
+     * proportional to the number of submissions.
+     *
+     * @return the number of queued submissions
+     */
+    public int getQueuedSubmissionCount() {
+        return submissionQueue.size();
+    }
+
+    /**
+     * Returns {@code true} if there are any tasks submitted to this
+     * pool that have not yet begun executing.
+     *
+     * @return {@code true} if there are any queued submissions
+     */
+    public boolean hasQueuedSubmissions() {
+        return !submissionQueue.isEmpty();
+    }
+
+    /**
+     * Removes and returns the next unexecuted submission if one is
+     * available.  This method may be useful in extensions to this
+     * class that re-assign work in systems with multiple pools.
+     *
+     * @return the next submission, or {@code null} if none
+     */
+    protected ForkJoinTask<?> pollSubmission() {
+        return submissionQueue.poll();
+    }
+
+    /**
+     * Removes all available unexecuted submitted and forked tasks
+     * from scheduling queues and adds them to the given collection,
+     * without altering their execution status. These may include
+     * artificially generated or wrapped tasks. This method is
+     * designed to be invoked only when the pool is known to be
+     * quiescent. Invocations at other times may not remove all
+     * tasks. A failure encountered while attempting to add elements
+     * to collection {@code c} may result in elements being in
+     * neither, either or both collections when the associated
+     * exception is thrown.  The behavior of this operation is
+     * undefined if the specified collection is modified while the
+     * operation is in progress.
+     *
+     * @param c the collection to transfer elements into
+     * @return the number of elements transferred
+     */
+    protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
+        int n = submissionQueue.drainTo(c);
+        ForkJoinWorkerThread[] ws = workers;
+        if (ws != null) {
+            for (int i = 0; i < ws.length; ++i) {
+                ForkJoinWorkerThread w = ws[i];
+                if (w != null)
+                    n += w.drainTasksTo(c);
+            }
+        }
+        return n;
+    }
+
+    /**
+     * Returns a string identifying this pool, as well as its state,
+     * including indications of run state, parallelism level, and
+     * worker and task counts.
+     *
+     * @return a string identifying this pool, as well as its state
+     */
+    public String toString() {
+        int ps = parallelism;
+        int wc = workerCounts;
+        int rc = runControl;
+        long st = getStealCount();
+        long qt = getQueuedTaskCount();
+        long qs = getQueuedSubmissionCount();
+        return super.toString() +
+            "[" + runStateToString(runStateOf(rc)) +
+            ", parallelism = " + ps +
+            ", size = " + totalCountOf(wc) +
+            ", active = " + activeCountOf(rc) +
+            ", running = " + runningCountOf(wc) +
+            ", steals = " + st +
+            ", tasks = " + qt +
+            ", submissions = " + qs +
+            "]";
+    }
+
+    private static String runStateToString(int rs) {
+        switch(rs) {
+        case RUNNING: return "Running";
+        case SHUTDOWN: return "Shutting down";
+        case TERMINATING: return "Terminating";
+        case TERMINATED: return "Terminated";
+        default: throw new Error("Unknown run state");
+        }
+    }
+
+    // lifecycle control
+
+    /**
+     * Initiates an orderly shutdown in which previously submitted
+     * tasks are executed, but no new tasks will be accepted.
+     * Invocation has no additional effect if already shut down.
+     * Tasks that are in the process of being submitted concurrently
+     * during the course of this method may or may not be rejected.
+     *
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public void shutdown() {
+        checkPermission();
+        transitionRunStateTo(SHUTDOWN);
+        if (canTerminateOnShutdown(runControl)) {
+            if (workers == null) { // shutting down before workers created
+                final ReentrantLock lock = this.workerLock;
+                lock.lock();
+                try {
+                    if (workers == null) {
+                        terminate();
+                        transitionRunStateTo(TERMINATED);
+                        termination.signalAll();
+                    }
+                } finally {
+                    lock.unlock();
+                }
+            }
+            terminateOnShutdown();
+        }
+    }
+
+    /**
+     * Attempts to cancel and/or stop all tasks, and reject all
+     * subsequently submitted tasks.  Tasks that are in the process of
+     * being submitted or executed concurrently during the course of
+     * this method may or may not be rejected. This method cancels
+     * both existing and unexecuted tasks, in order to permit
+     * termination in the presence of task dependencies. So the method
+     * always returns an empty list (unlike the case for some other
+     * Executors).
+     *
+     * @return an empty list
+     * @throws SecurityException if a security manager exists and
+     *         the caller is not permitted to modify threads
+     *         because it does not hold {@link
+     *         java.lang.RuntimePermission}{@code ("modifyThread")}
+     */
+    public List<Runnable> shutdownNow() {
+        checkPermission();
+        terminate();
+        return Collections.emptyList();
+    }
+
+    /**
+     * Returns {@code true} if all tasks have completed following shut down.
+     *
+     * @return {@code true} if all tasks have completed following shut down
+     */
+    public boolean isTerminated() {
+        return runStateOf(runControl) == TERMINATED;
+    }
+
+    /**
+     * Returns {@code true} if the process of termination has
+     * commenced but not yet completed.  This method may be useful for
+     * debugging. A return of {@code true} reported a sufficient
+     * period after shutdown may indicate that submitted tasks have
+     * ignored or suppressed interruption, causing this executor not
+     * to properly terminate.
+     *
+     * @return {@code true} if terminating but not yet terminated
+     */
+    public boolean isTerminating() {
+        return runStateOf(runControl) == TERMINATING;
+    }
+
+    /**
+     * Returns {@code true} if this pool has been shut down.
+     *
+     * @return {@code true} if this pool has been shut down
+     */
+    public boolean isShutdown() {
+        return runStateOf(runControl) >= SHUTDOWN;
+    }
+
+    /**
+     * Returns true if pool is not terminating or terminated.
+     * Used internally to suppress execution when terminating.
+     */
+    final boolean isProcessingTasks() {
+        return runStateOf(runControl) < TERMINATING;
+    }
+
+    /**
+     * Blocks until all tasks have completed execution after a shutdown
+     * request, or the timeout occurs, or the current thread is
+     * interrupted, whichever happens first.
+     *
+     * @param timeout the maximum time to wait
+     * @param unit the time unit of the timeout argument
+     * @return {@code true} if this executor terminated and
+     *         {@code false} if the timeout elapsed before termination
+     * @throws InterruptedException if interrupted while waiting
+     */
+    public boolean awaitTermination(long timeout, TimeUnit unit)
+        throws InterruptedException {
+        long nanos = unit.toNanos(timeout);
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            for (;;) {
+                if (isTerminated())
+                    return true;
+                if (nanos <= 0)
+                    return false;
+                nanos = termination.awaitNanos(nanos);
+            }
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    // Shutdown and termination support
+
+    /**
+     * Callback from terminating worker. Nulls out the corresponding
+     * workers slot, and if terminating, tries to terminate; else
+     * tries to shrink workers array.
+     *
+     * @param w the worker
+     */
+    final void workerTerminated(ForkJoinWorkerThread w) {
+        updateStealCount(w);
+        updateWorkerCount(-1);
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            ForkJoinWorkerThread[] ws = workers;
+            if (ws != null) {
+                int idx = w.poolIndex;
+                if (idx >= 0 && idx < ws.length && ws[idx] == w)
+                    ws[idx] = null;
+                if (totalCountOf(workerCounts) == 0) {
+                    terminate(); // no-op if already terminating
+                    transitionRunStateTo(TERMINATED);
+                    termination.signalAll();
+                }
+                else if (isProcessingTasks()) {
+                    tryShrinkWorkerArray();
+                    tryResumeSpare(true); // allow replacement
+                }
+            }
+        } finally {
+            lock.unlock();
+        }
+        signalIdleWorkers();
+    }
+
+    /**
+     * Initiates termination.
+     */
+    private void terminate() {
+        if (transitionRunStateTo(TERMINATING)) {
+            stopAllWorkers();
+            resumeAllSpares();
+            signalIdleWorkers();
+            cancelQueuedSubmissions();
+            cancelQueuedWorkerTasks();
+            interruptUnterminatedWorkers();
+            signalIdleWorkers(); // resignal after interrupt
+        }
+    }
+
+    /**
+     * Possibly terminates when on shutdown state.
+     */
+    private void terminateOnShutdown() {
+        if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
+            terminate();
+    }
+
+    /**
+     * Clears out and cancels submissions.
+     */
+    private void cancelQueuedSubmissions() {
+        ForkJoinTask<?> task;
+        while ((task = pollSubmission()) != null)
+            task.cancel(false);
+    }
+
+    /**
+     * Cleans out worker queues.
+     */
+    private void cancelQueuedWorkerTasks() {
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            ForkJoinWorkerThread[] ws = workers;
+            if (ws != null) {
+                for (int i = 0; i < ws.length; ++i) {
+                    ForkJoinWorkerThread t = ws[i];
+                    if (t != null)
+                        t.cancelTasks();
+                }
+            }
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Sets each worker's status to terminating. Requires lock to avoid
+     * conflicts with add/remove.
+     */
+    private void stopAllWorkers() {
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            ForkJoinWorkerThread[] ws = workers;
+            if (ws != null) {
+                for (int i = 0; i < ws.length; ++i) {
+                    ForkJoinWorkerThread t = ws[i];
+                    if (t != null)
+                        t.shutdownNow();
+                }
+            }
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    /**
+     * Interrupts all unterminated workers.  This is not required for
+     * sake of internal control, but may help unstick user code during
+     * shutdown.
+     */
+    private void interruptUnterminatedWorkers() {
+        final ReentrantLock lock = this.workerLock;
+        lock.lock();
+        try {
+            ForkJoinWorkerThread[] ws = workers;
+            if (ws != null) {
+                for (int i = 0; i < ws.length; ++i) {
+                    ForkJoinWorkerThread t = ws[i];
+                    if (t != null && !t.isTerminated()) {
+                        try {
+                            t.interrupt();
+                        } catch (SecurityException ignore) {
+                        }
+                    }
+                }
+            }
+        } finally {
+            lock.unlock();
+        }
+    }
+
+
+    /*
+     * Nodes for event barrier to manage idle threads.  Queue nodes
+     * are basic Treiber stack nodes, also used for spare stack.
+     *
+     * The event barrier has an event count and a wait queue (actually
+     * a Treiber stack).  Workers are enabled to look for work when
+     * the eventCount is incremented. If they fail to find work, they
+     * may wait for next count. Upon release, threads help others wake
+     * up.
+     *
+     * Synchronization events occur only in enough contexts to
+     * maintain overall liveness:
+     *
+     *   - Submission of a new task to the pool
+     *   - Resizes or other changes to the workers array
+     *   - pool termination
+     *   - A worker pushing a task on an empty queue
+     *
+     * The case of pushing a task occurs often enough, and is heavy
+     * enough compared to simple stack pushes, to require special
+     * handling: Method signalWork returns without advancing count if
+     * the queue appears to be empty.  This would ordinarily result in
+     * races causing some queued waiters not to be woken up. To avoid
+     * this, the first worker enqueued in method sync (see
+     * syncIsReleasable) rescans for tasks after being enqueued, and
+     * helps signal if any are found. This works well because the
+     * worker has nothing better to do, and so might as well help
+     * alleviate the overhead and contention on the threads actually
+     * doing work.  Also, since event counts increments on task
+     * availability exist to maintain liveness (rather than to force
+     * refreshes etc), it is OK for callers to exit early if
+     * contending with another signaller.
+     */
+    static final class WaitQueueNode {
+        WaitQueueNode next; // only written before enqueued
+        volatile ForkJoinWorkerThread thread; // nulled to cancel wait
+        final long count; // unused for spare stack
+
+        WaitQueueNode(long c, ForkJoinWorkerThread w) {
+            count = c;
+            thread = w;
+        }
+
+        /**
+         * Wakes up waiter, returning false if known to already
+         */
+        boolean signal() {
+            ForkJoinWorkerThread t = thread;
+            if (t == null)
+                return false;
+            thread = null;
+            LockSupport.unpark(t);
+            return true;
+        }
+
+        /**
+         * Awaits release on sync.
+         */
+        void awaitSyncRelease(ForkJoinPool p) {
+            while (thread != null && !p.syncIsReleasable(this))
+                LockSupport.park(this);
+        }
+
+        /**
+         * Awaits resumption as spare.
+         */
+        void awaitSpareRelease() {
+            while (thread != null) {
+                if (!Thread.interrupted())
+                    LockSupport.park(this);
+            }
+        }
+    }
+
+    /**
+     * Ensures that no thread is waiting for count to advance from the
+     * current value of eventCount read on entry to this method, by
+     * releasing waiting threads if necessary.
+     *
+     * @return the count
+     */
+    final long ensureSync() {
+        long c = eventCount;
+        WaitQueueNode q;
+        while ((q = syncStack) != null && q.count < c) {
+            if (casBarrierStack(q, null)) {
+                do {
+                    q.signal();
+                } while ((q = q.next) != null);
+                break;
+            }
+        }
+        return c;
+    }
+
+    /**
+     * Increments event count and releases waiting threads.
+     */
+    private void signalIdleWorkers() {
+        long c;
+        do {} while (!casEventCount(c = eventCount, c+1));
+        ensureSync();
+    }
+
+    /**
+     * Signals threads waiting to poll a task. Because method sync
+     * rechecks availability, it is OK to only proceed if queue
+     * appears to be non-empty, and OK to skip under contention to
+     * increment count (since some other thread succeeded).
+     */
+    final void signalWork() {
+        long c;
+        WaitQueueNode q;
+        if (syncStack != null &&
+            casEventCount(c = eventCount, c+1) &&
+            (((q = syncStack) != null && q.count <= c) &&
+             (!casBarrierStack(q, q.next) || !q.signal())))
+            ensureSync();
+    }
+
+    /**
+     * Waits until event count advances from last value held by
+     * caller, or if excess threads, caller is resumed as spare, or
+     * caller or pool is terminating. Updates caller's event on exit.
+     *
+     * @param w the calling worker thread
+     */
+    final void sync(ForkJoinWorkerThread w) {
+        updateStealCount(w); // Transfer w's count while it is idle
+
+        while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
+            long prev = w.lastEventCount;
+            WaitQueueNode node = null;
+            WaitQueueNode h;
+            while (eventCount == prev &&
+                   ((h = syncStack) == null || h.count == prev)) {
+                if (node == null)
+                    node = new WaitQueueNode(prev, w);
+                if (casBarrierStack(node.next = h, node)) {
+                    node.awaitSyncRelease(this);
+                    break;
+                }
+            }
+            long ec = ensureSync();
+            if (ec != prev) {
+                w.lastEventCount = ec;
+                break;
+            }
+        }
+    }
+
+    /**
+     * Returns {@code true} if worker waiting on sync can proceed:
+     *  - on signal (thread == null)
+     *  - on event count advance (winning race to notify vs signaller)
+     *  - on interrupt
+     *  - if the first queued node, we find work available
+     * If node was not signalled and event count not advanced on exit,
+     * then we also help advance event count.
+     *
+     * @return {@code true} if node can be released
+     */
+    final boolean syncIsReleasable(WaitQueueNode node) {
+        long prev = node.count;
+        if (!Thread.interrupted() && node.thread != null &&
+            (node.next != null ||
+             !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
+            eventCount == prev)
+            return false;
+        if (node.thread != null) {
+            node.thread = null;
+            long ec = eventCount;
+            if (prev <= ec) // help signal
+                casEventCount(ec, ec+1);
+        }
+        return true;
+    }
+
+    /**
+     * Returns {@code true} if a new sync event occurred since last
+     * call to sync or this method, if so, updating caller's count.
+     */
+    final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
+        long lc = w.lastEventCount;
+        long ec = ensureSync();
+        if (ec == lc)
+            return false;
+        w.lastEventCount = ec;
+        return true;
+    }
+
+    //  Parallelism maintenance
+
+    /**
+     * Decrements running count; if too low, adds spare.
+     *
+     * Conceptually, all we need to do here is add or resume a
+     * spare thread when one is about to block (and remove or
+     * suspend it later when unblocked -- see suspendIfSpare).
+     * However, implementing this idea requires coping with
+     * several problems: we have imperfect information about the
+     * states of threads. Some count updates can and usually do
+     * lag run state changes, despite arrangements to keep them
+     * accurate (for example, when possible, updating counts
+     * before signalling or resuming), especially when running on
+     * dynamic JVMs that don't optimize the infrequent paths that
+     * update counts. Generating too many threads can make these
+     * problems become worse, because excess threads are more
+     * likely to be context-switched with others, slowing them all
+     * down, especially if there is no work available, so all are
+     * busy scanning or idling.  Also, excess spare threads can
+     * only be suspended or removed when they are idle, not
+     * immediately when they aren't needed. So adding threads will
+     * raise parallelism level for longer than necessary.  Also,
+     * FJ applications often encounter highly transient peaks when
+     * many threads are blocked joining, but for less time than it
+     * takes to create or resume spares.
+     *
+     * @param joinMe if non-null, return early if done
+     * @param maintainParallelism if true, try to stay within
+     * target counts, else create only to avoid starvation
+     * @return true if joinMe known to be done
+     */
+    final boolean preJoin(ForkJoinTask<?> joinMe,
+                          boolean maintainParallelism) {
+        maintainParallelism &= maintainsParallelism; // overrride
+        boolean dec = false;  // true when running count decremented
+        while (spareStack == null || !tryResumeSpare(dec)) {
+            int counts = workerCounts;
+            if (dec || (dec = casWorkerCounts(counts, --counts))) {
+                if (!needSpare(counts, maintainParallelism))
+                    break;
+                if (joinMe.status < 0)
+                    return true;
+                if (tryAddSpare(counts))
+                    break;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Same idea as preJoin
+     */
+    final boolean preBlock(ManagedBlocker blocker,
+                           boolean maintainParallelism) {
+        maintainParallelism &= maintainsParallelism;
+        boolean dec = false;
+        while (spareStack == null || !tryResumeSpare(dec)) {
+            int counts = workerCounts;
+            if (dec || (dec = casWorkerCounts(counts, --counts))) {
+                if (!needSpare(counts, maintainParallelism))
+                    break;
+                if (blocker.isReleasable())
+                    return true;
+                if (tryAddSpare(counts))
+                    break;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Returns {@code true} if a spare thread appears to be needed.
+     * If maintaining parallelism, returns true when the deficit in
+     * running threads is more than the surplus of total threads, and
+     * there is apparently some work to do.  This self-limiting rule
+     * means that the more threads that have already been added, the
+     * less parallelism we will tolerate before adding another.
+     *
+     * @param counts current worker counts
+     * @param maintainParallelism try to maintain parallelism
+     */
+    private boolean needSpare(int counts, boolean maintainParallelism) {
+        int ps = parallelism;
+        int rc = runningCountOf(counts);
+        int tc = totalCountOf(counts);
+        int runningDeficit = ps - rc;
+        int totalSurplus = tc - ps;
+        return (tc < maxPoolSize &&
+                (rc == 0 || totalSurplus < 0 ||
+                 (maintainParallelism &&
+                  runningDeficit > totalSurplus &&
+                  ForkJoinWorkerThread.hasQueuedTasks(workers))));
+    }
+
+    /**
+     * Adds a spare worker if lock available and no more than the
+     * expected numbers of threads exist.
+     *
+     * @return true if successful
+     */
+    private boolean tryAddSpare(int expectedCounts) {
+        final ReentrantLock lock = this.workerLock;
+        int expectedRunning = runningCountOf(expectedCounts);
+        int expectedTotal = totalCountOf(expectedCounts);
+        boolean success = false;
+        boolean locked = false;
+        // confirm counts while locking; CAS after obtaining lock
+        try {
+            for (;;) {
+                int s = workerCounts;
+                int tc = totalCountOf(s);
+                int rc = runningCountOf(s);
+                if (rc > expectedRunning || tc > expectedTotal)
+                    break;
+                if (!locked && !(locked = lock.tryLock()))
+                    break;
+                if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
+                    createAndStartSpare(tc);
+                    success = true;
+                    break;
+                }
+            }
+        } finally {
+            if (locked)
+                lock.unlock();
+        }
+        return success;
+    }
+
+    /**
+     * Adds the kth spare worker. On entry, pool counts are already
+     * adjusted to reflect addition.
+     */
+    private void createAndStartSpare(int k) {
+        ForkJoinWorkerThread w = null;
+        ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
+        int len = ws.length;
+        // Probably, we can place at slot k. If not, find empty slot
+        if (k < len && ws[k] != null) {
+            for (k = 0; k < len && ws[k] != null; ++k)
+                ;
+        }
+        if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
+            ws[k] = w;
+            w.start();
+        }
+        else
+            updateWorkerCount(-1); // adjust on failure
+        signalIdleWorkers();
+    }
+
+    /**
+     * Suspends calling thread w if there are excess threads.  Called
+     * only from sync.  Spares are enqueued in a Treiber stack using
+     * the same WaitQueueNodes as barriers.  They are resumed mainly
+     * in preJoin, but are also woken on pool events that require all
+     * threads to check run state.
+     *
+     * @param w the caller
+     */
+    private boolean suspendIfSpare(ForkJoinWorkerThread w) {
+        WaitQueueNode node = null;
+        int s;
+        while (parallelism < runningCountOf(s = workerCounts)) {
+            if (node == null)
+                node = new WaitQueueNode(0, w);
+            if (casWorkerCounts(s, s-1)) { // representation-dependent
+                // push onto stack
+                do {} while (!casSpareStack(node.next = spareStack, node));
+                // block until released by resumeSpare
+                node.awaitSpareRelease();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Tries to pop and resume a spare thread.
+     *
+     * @param updateCount if true, increment running count on success
+     * @return true if successful
+     */
+    private boolean tryResumeSpare(boolean updateCount) {
+        WaitQueueNode q;
+        while ((q = spareStack) != null) {
+            if (casSpareStack(q, q.next)) {
+                if (updateCount)
+                    updateRunningCount(1);
+                q.signal();
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Pops and resumes all spare threads. Same idea as ensureSync.
+     *
+     * @return true if any spares released
+     */
+    private boolean resumeAllSpares() {
+        WaitQueueNode q;
+        while ( (q = spareStack) != null) {
+            if (casSpareStack(q, null)) {
+                do {
+                    updateRunningCount(1);
+                    q.signal();
+                } while ((q = q.next) != null);
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Pops and shuts down excessive spare threads. Call only while
+     * holding lock. This is not guaranteed to eliminate all excess
+     * threads, only those suspended as spares, which are the ones
+     * unlikely to be needed in the future.
+     */
+    private void trimSpares() {
+        int surplus = totalCountOf(workerCounts) - parallelism;
+        WaitQueueNode q;
+        while (surplus > 0 && (q = spareStack) != null) {
+            if (casSpareStack(q, null)) {
+                do {
+                    updateRunningCount(1);
+                    ForkJoinWorkerThread w = q.thread;
+                    if (w != null && surplus > 0 &&
+                        runningCountOf(workerCounts) > 0 && w.shutdown())
+                        --surplus;
+                    q.signal();
+                } while ((q = q.next) != null);
+            }
+        }
+    }
+
+    /**
+     * Interface for extending managed parallelism for tasks running
+     * in {@link ForkJoinPool}s.
+     *
+     * <p>A {@code ManagedBlocker} provides two methods.
+     * Method {@code isReleasable} must return {@code true} if
+     * blocking is not necessary. Method {@code block} blocks the
+     * current thread if necessary (perhaps internally invoking
+     * {@code isReleasable} before actually blocking).
+     *
+     * <p>For example, here is a ManagedBlocker based on a
+     * ReentrantLock:
+     *  <pre> {@code
+     * class ManagedLocker implements ManagedBlocker {
+     *   final ReentrantLock lock;
+     *   boolean hasLock = false;
+     *   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
+     *   public boolean block() {
+     *     if (!hasLock)
+     *       lock.lock();
+     *     return true;
+     *   }
+     *   public boolean isReleasable() {
+     *     return hasLock || (hasLock = lock.tryLock());
+     *   }
+     * }}</pre>
+     */
+    public static interface ManagedBlocker {
+        /**
+         * Possibly blocks the current thread, for example waiting for
+         * a lock or condition.
+         *
+         * @return {@code true} if no additional blocking is necessary
+         * (i.e., if isReleasable would return true)
+         * @throws InterruptedException if interrupted while waiting
+         * (the method is not required to do so, but is allowed to)
+         */
+        boolean block() throws InterruptedException;
+
+        /**
+         * Returns {@code true} if blocking is unnecessary.
+         */
+        boolean isReleasable();
+    }
+
+    /**
+     * Blocks in accord with the given blocker.  If the current thread
+     * is a {@link ForkJoinWorkerThread}, this method possibly
+     * arranges for a spare thread to be activated if necessary to
+     * ensure parallelism while the current thread is blocked.
+     *
+     * <p>If {@code maintainParallelism} is {@code true} and the pool
+     * supports it ({@link #getMaintainsParallelism}), this method
+     * attempts to maintain the pool's nominal parallelism. Otherwise
+     * it activates a thread only if necessary to avoid complete
+     * starvation. This option may be preferable when blockages use
+     * timeouts, or are almost always brief.
+     *
+     * <p>If the caller is not a {@link ForkJoinTask}, this method is
+     * behaviorally equivalent to
+     *  <pre> {@code
+     * while (!blocker.isReleasable())
+     *   if (blocker.block())
+     *     return;
+     * }</pre>
+     *
+     * If the caller is a {@code ForkJoinTask}, then the pool may
+     * first be expanded to ensure parallelism, and later adjusted.
+     *
+     * @param blocker the blocker
+     * @param maintainParallelism if {@code true} and supported by
+     * this pool, attempt to maintain the pool's nominal parallelism;
+     * otherwise activate a thread only if necessary to avoid
+     * complete starvation.
+     * @throws InterruptedException if blocker.block did so
+     */
+    public static void managedBlock(ManagedBlocker blocker,
+                                    boolean maintainParallelism)
+        throws InterruptedException {
+        Thread t = Thread.currentThread();
+        ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
+                             ((ForkJoinWorkerThread) t).pool : null);
+        if (!blocker.isReleasable()) {
+            try {
+                if (pool == null ||
+                    !pool.preBlock(blocker, maintainParallelism))
+                    awaitBlocker(blocker);
+            } finally {
+                if (pool != null)
+                    pool.updateRunningCount(1);
+            }
+        }
+    }
+
+    private static void awaitBlocker(ManagedBlocker blocker)
+        throws InterruptedException {
+        do {} while (!blocker.isReleasable() && !blocker.block());
+    }
+
+    // AbstractExecutorService overrides.  These rely on undocumented
+    // fact that ForkJoinTask.adapt returns ForkJoinTasks that also
+    // implement RunnableFuture.
+
+    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
+        return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
+    }
+
+    protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
+        return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
+    }
+
+    // Unsafe mechanics
+
+    private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+    private static final long eventCountOffset =
+        objectFieldOffset("eventCount", ForkJoinPool.class);
+    private static final long workerCountsOffset =
+        objectFieldOffset("workerCounts", ForkJoinPool.class);
+    private static final long runControlOffset =
+        objectFieldOffset("runControl", ForkJoinPool.class);
+    private static final long syncStackOffset =
+        objectFieldOffset("syncStack",ForkJoinPool.class);
+    private static final long spareStackOffset =
+        objectFieldOffset("spareStack", ForkJoinPool.class);
+
+    private boolean casEventCount(long cmp, long val) {
+        return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
+    }
+    private boolean casWorkerCounts(int cmp, int val) {
+        return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
+    }
+    private boolean casRunControl(int cmp, int val) {
+        return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
+    }
+    private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
+        return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
+    }
+    private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
+        return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
+    }
+
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to corresponding Error
+            NoSuchFieldError error = new NoSuchFieldError(field);
+            error.initCause(e);
+            throw error;
+        }
+    }
+}

src/share/classes/java/util/concurrent/ForkJoinTask.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.RandomAccess;
+import java.util.Map;
+import java.util.WeakHashMap;
+
+/**
+ * Abstract base class for tasks that run within a {@link ForkJoinPool}.
+ * A {@code ForkJoinTask} is a thread-like entity that is much
+ * lighter weight than a normal thread.  Huge numbers of tasks and
+ * subtasks may be hosted by a small number of actual threads in a
+ * ForkJoinPool, at the price of some usage limitations.
+ *
+ * <p>A "main" {@code ForkJoinTask} begins execution when submitted
+ * to a {@link ForkJoinPool}.  Once started, it will usually in turn
+ * start other subtasks.  As indicated by the name of this class,
+ * many programs using {@code ForkJoinTask} employ only methods
+ * {@link #fork} and {@link #join}, or derivatives such as {@link
+ * #invokeAll}.  However, this class also provides a number of other
+ * methods that can come into play in advanced usages, as well as
+ * extension mechanics that allow support of new forms of fork/join
+ * processing.
+ *
+ * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
+ * The efficiency of {@code ForkJoinTask}s stems from a set of
+ * restrictions (that are only partially statically enforceable)
+ * reflecting their intended use as computational tasks calculating
+ * pure functions or operating on purely isolated objects.  The
+ * primary coordination mechanisms are {@link #fork}, that arranges
+ * asynchronous execution, and {@link #join}, that doesn't proceed
+ * until the task's result has been computed.  Computations should
+ * avoid {@code synchronized} methods or blocks, and should minimize
+ * other blocking synchronization apart from joining other tasks or
+ * using synchronizers such as Phasers that are advertised to
+ * cooperate with fork/join scheduling. Tasks should also not perform
+ * blocking IO, and should ideally access variables that are
+ * completely independent of those accessed by other running
+ * tasks. Minor breaches of these restrictions, for example using
+ * shared output streams, may be tolerable in practice, but frequent
+ * use may result in poor performance, and the potential to
+ * indefinitely stall if the number of threads not waiting for IO or
+ * other external synchronization becomes exhausted. This usage
+ * restriction is in part enforced by not permitting checked
+ * exceptions such as {@code IOExceptions} to be thrown. However,
+ * computations may still encounter unchecked exceptions, that are
+ * rethrown to callers attempting to join them. These exceptions may
+ * additionally include {@link RejectedExecutionException} stemming
+ * from internal resource exhaustion, such as failure to allocate
+ * internal task queues.
+ *
+ * <p>The primary method for awaiting completion and extracting
+ * results of a task is {@link #join}, but there are several variants:
+ * The {@link Future#get} methods support interruptible and/or timed
+ * waits for completion and report results using {@code Future}
+ * conventions. Method {@link #helpJoin} enables callers to actively
+ * execute other tasks while awaiting joins, which is sometimes more
+ * efficient but only applies when all subtasks are known to be
+ * strictly tree-structured. Method {@link #invoke} is semantically
+ * equivalent to {@code fork(); join()} but always attempts to begin
+ * execution in the current thread. The "<em>quiet</em>" forms of
+ * these methods do not extract results or report exceptions. These
+ * may be useful when a set of tasks are being executed, and you need
+ * to delay processing of results or exceptions until all complete.
+ * Method {@code invokeAll} (available in multiple versions)
+ * performs the most common form of parallel invocation: forking a set
+ * of tasks and joining them all.
+ *
+ * <p>The execution status of tasks may be queried at several levels
+ * of detail: {@link #isDone} is true if a task completed in any way
+ * (including the case where a task was cancelled without executing);
+ * {@link #isCompletedNormally} is true if a task completed without
+ * cancellation or encountering an exception; {@link #isCancelled} is
+ * true if the task was cancelled (in which case {@link #getException}
+ * returns a {@link java.util.concurrent.CancellationException}); and
+ * {@link #isCompletedAbnormally} is true if a task was either
+ * cancelled or encountered an exception, in which case {@link
+ * #getException} will return either the encountered exception or
+ * {@link java.util.concurrent.CancellationException}.
+ *
+ * <p>The ForkJoinTask class is not usually directly subclassed.
+ * Instead, you subclass one of the abstract classes that support a
+ * particular style of fork/join processing, typically {@link
+ * RecursiveAction} for computations that do not return results, or
+ * {@link RecursiveTask} for those that do.  Normally, a concrete
+ * ForkJoinTask subclass declares fields comprising its parameters,
+ * established in a constructor, and then defines a {@code compute}
+ * method that somehow uses the control methods supplied by this base
+ * class. While these methods have {@code public} access (to allow
+ * instances of different task subclasses to call each other's
+ * methods), some of them may only be called from within other
+ * ForkJoinTasks (as may be determined using method {@link
+ * #inForkJoinPool}).  Attempts to invoke them in other contexts
+ * result in exceptions or errors, possibly including
+ * ClassCastException.
+ *
+ * <p>Most base support methods are {@code final}, to prevent
+ * overriding of implementations that are intrinsically tied to the
+ * underlying lightweight task scheduling framework.  Developers
+ * creating new basic styles of fork/join processing should minimally
+ * implement {@code protected} methods {@link #exec}, {@link
+ * #setRawResult}, and {@link #getRawResult}, while also introducing
+ * an abstract computational method that can be implemented in its
+ * subclasses, possibly relying on other {@code protected} methods
+ * provided by this class.
+ *
+ * <p>ForkJoinTasks should perform relatively small amounts of
+ * computation. Large tasks should be split into smaller subtasks,
+ * usually via recursive decomposition. As a very rough rule of thumb,
+ * a task should perform more than 100 and less than 10000 basic
+ * computational steps. If tasks are too big, then parallelism cannot
+ * improve throughput. If too small, then memory and internal task
+ * maintenance overhead may overwhelm processing.
+ *
+ * <p>This class provides {@code adapt} methods for {@link Runnable}
+ * and {@link Callable}, that may be of use when mixing execution of
+ * {@code ForkJoinTasks} with other kinds of tasks. When all tasks
+ * are of this form, consider using a pool in
+ * {@linkplain ForkJoinPool#setAsyncMode async mode}.
+ *
+ * <p>ForkJoinTasks are {@code Serializable}, which enables them to be
+ * used in extensions such as remote execution frameworks. It is
+ * sensible to serialize tasks only before or after, but not during,
+ * execution. Serialization is not relied on during execution itself.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
+
+    /**
+     * Run control status bits packed into a single int to minimize
+     * footprint and to ensure atomicity (via CAS).  Status is
+     * initially zero, and takes on nonnegative values until
+     * completed, upon which status holds COMPLETED. CANCELLED, or
+     * EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
+     * blocking waits by other threads have SIGNAL_MASK bits set --
+     * bit 15 for external (nonFJ) waits, and the rest a count of
+     * waiting FJ threads.  (This representation relies on
+     * ForkJoinPool max thread limits). Completion of a stolen task
+     * with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
+     * though suboptimal for some purposes, we use basic builtin
+     * wait/notify to take advantage of "monitor inflation" in JVMs
+     * that we would otherwise need to emulate to avoid adding further
+     * per-task bookkeeping overhead. Note that bits 16-28 are
+     * currently unused. Also value 0x80000000 is available as spare
+     * completion value.
+     */
+    volatile int status; // accessed directly by pool and workers
+
+    static final int COMPLETION_MASK      = 0xe0000000;
+    static final int NORMAL               = 0xe0000000; // == mask
+    static final int CANCELLED            = 0xc0000000;
+    static final int EXCEPTIONAL          = 0xa0000000;
+    static final int SIGNAL_MASK          = 0x0000ffff;
+    static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
+    static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
+
+    /**
+     * Table of exceptions thrown by tasks, to enable reporting by
+     * callers. Because exceptions are rare, we don't directly keep
+     * them with task objects, but instead use a weak ref table.  Note
+     * that cancellation exceptions don't appear in the table, but are
+     * instead recorded as status values.
+     * TODO: Use ConcurrentReferenceHashMap
+     */
+    static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
+        Collections.synchronizedMap
+        (new WeakHashMap<ForkJoinTask<?>, Throwable>());
+
+    // within-package utilities
+
+    /**
+     * Gets current worker thread, or null if not a worker thread.
+     */
+    static ForkJoinWorkerThread getWorker() {
+        Thread t = Thread.currentThread();
+        return ((t instanceof ForkJoinWorkerThread) ?
+                (ForkJoinWorkerThread) t : null);
+    }
+
+    final boolean casStatus(int cmp, int val) {
+        return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
+    }
+
+    /**
+     * Workaround for not being able to rethrow unchecked exceptions.
+     */
+    static void rethrowException(Throwable ex) {
+        if (ex != null)
+            UNSAFE.throwException(ex);
+    }
+
+    // Setting completion status
+
+    /**
+     * Marks completion and wakes up threads waiting to join this task.
+     *
+     * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
+     */
+    final void setCompletion(int completion) {
+        ForkJoinPool pool = getPool();
+        if (pool != null) {
+            int s; // Clear signal bits while setting completion status
+            do {} while ((s = status) >= 0 && !casStatus(s, completion));
+
+            if ((s & SIGNAL_MASK) != 0) {
+                if ((s &= INTERNAL_SIGNAL_MASK) != 0)
+                    pool.updateRunningCount(s);
+                synchronized (this) { notifyAll(); }
+            }
+        }
+        else
+            externallySetCompletion(completion);
+    }
+
+    /**
+     * Version of setCompletion for non-FJ threads.  Leaves signal
+     * bits for unblocked threads to adjust, and always notifies.
+     */
+    private void externallySetCompletion(int completion) {
+        int s;
+        do {} while ((s = status) >= 0 &&
+                     !casStatus(s, (s & SIGNAL_MASK) | completion));
+        synchronized (this) { notifyAll(); }
+    }
+
+    /**
+     * Sets status to indicate normal completion.
+     */
+    final void setNormalCompletion() {
+        // Try typical fast case -- single CAS, no signal, not already done.
+        // Manually expand casStatus to improve chances of inlining it
+        if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
+            setCompletion(NORMAL);
+    }
+
+    // internal waiting and notification
+
+    /**
+     * Performs the actual monitor wait for awaitDone.
+     */
+    private void doAwaitDone() {
+        // Minimize lock bias and in/de-flation effects by maximizing
+        // chances of waiting inside sync
+        try {
+            while (status >= 0)
+                synchronized (this) { if (status >= 0) wait(); }
+        } catch (InterruptedException ie) {
+            onInterruptedWait();
+        }
+    }
+
+    /**
+     * Performs the actual timed monitor wait for awaitDone.
+     */
+    private void doAwaitDone(long startTime, long nanos) {
+        synchronized (this) {
+            try {
+                while (status >= 0) {
+                    long nt = nanos - (System.nanoTime() - startTime);
+                    if (nt <= 0)
+                        break;
+                    wait(nt / 1000000, (int) (nt % 1000000));
+                }
+            } catch (InterruptedException ie) {
+                onInterruptedWait();
+            }
+        }
+    }
+
+    // Awaiting completion
+
+    /**
+     * Sets status to indicate there is joiner, then waits for join,
+     * surrounded with pool notifications.
+     *
+     * @return status upon exit
+     */
+    private int awaitDone(ForkJoinWorkerThread w,
+                          boolean maintainParallelism) {
+        ForkJoinPool pool = (w == null) ? null : w.pool;
+        int s;
+        while ((s = status) >= 0) {
+            if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
+                if (pool == null || !pool.preJoin(this, maintainParallelism))
+                    doAwaitDone();
+                if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
+                    adjustPoolCountsOnUnblock(pool);
+                break;
+            }
+        }
+        return s;
+    }
+
+    /**
+     * Timed version of awaitDone
+     *
+     * @return status upon exit
+     */
+    private int awaitDone(ForkJoinWorkerThread w, long nanos) {
+        ForkJoinPool pool = (w == null) ? null : w.pool;
+        int s;
+        while ((s = status) >= 0) {
+            if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
+                long startTime = System.nanoTime();
+                if (pool == null || !pool.preJoin(this, false))
+                    doAwaitDone(startTime, nanos);
+                if ((s = status) >= 0) {
+                    adjustPoolCountsOnCancelledWait(pool);
+                    s = status;
+                }
+                if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
+                    adjustPoolCountsOnUnblock(pool);
+                break;
+            }
+        }
+        return s;
+    }
+
+    /**
+     * Notifies pool that thread is unblocked. Called by signalled
+     * threads when woken by non-FJ threads (which is atypical).
+     */
+    private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
+        int s;
+        do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
+        if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
+            pool.updateRunningCount(s);
+    }
+
+    /**
+     * Notifies pool to adjust counts on cancelled or timed out wait.
+     */
+    private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
+        if (pool != null) {
+            int s;
+            while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
+                if (casStatus(s, s - 1)) {
+                    pool.updateRunningCount(1);
+                    break;
+                }
+            }
+        }
+    }
+
+    /**
+     * Handles interruptions during waits.
+     */
+    private void onInterruptedWait() {
+        ForkJoinWorkerThread w = getWorker();
+        if (w == null)
+            Thread.currentThread().interrupt(); // re-interrupt
+        else if (w.isTerminating())
+            cancelIgnoringExceptions();
+        // else if FJworker, ignore interrupt
+    }
+
+    // Recording and reporting exceptions
+
+    private void setDoneExceptionally(Throwable rex) {
+        exceptionMap.put(this, rex);
+        setCompletion(EXCEPTIONAL);
+    }
+
+    /**
+     * Throws the exception associated with status s.
+     *
+     * @throws the exception
+     */
+    private void reportException(int s) {
+        if ((s &= COMPLETION_MASK) < NORMAL) {
+            if (s == CANCELLED)
+                throw new CancellationException();
+            else
+                rethrowException(exceptionMap.get(this));
+        }
+    }
+
+    /**
+     * Returns result or throws exception using j.u.c.Future conventions.
+     * Only call when {@code isDone} known to be true or thread known
+     * to be interrupted.
+     */
+    private V reportFutureResult()
+        throws InterruptedException, ExecutionException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        int s = status & COMPLETION_MASK;
+        if (s < NORMAL) {
+            Throwable ex;
+            if (s == CANCELLED)
+                throw new CancellationException();
+            if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+                throw new ExecutionException(ex);
+        }
+        return getRawResult();
+    }
+
+    /**
+     * Returns result or throws exception using j.u.c.Future conventions
+     * with timeouts.
+     */
+    private V reportTimedFutureResult()
+        throws InterruptedException, ExecutionException, TimeoutException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        Throwable ex;
+        int s = status & COMPLETION_MASK;
+        if (s == NORMAL)
+            return getRawResult();
+        else if (s == CANCELLED)
+            throw new CancellationException();
+        else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
+            throw new ExecutionException(ex);
+        else
+            throw new TimeoutException();
+    }
+
+    // internal execution methods
+
+    /**
+     * Calls exec, recording completion, and rethrowing exception if
+     * encountered. Caller should normally check status before calling.
+     *
+     * @return true if completed normally
+     */
+    private boolean tryExec() {
+        try { // try block must contain only call to exec
+            if (!exec())
+                return false;
+        } catch (Throwable rex) {
+            setDoneExceptionally(rex);
+            rethrowException(rex);
+            return false; // not reached
+        }
+        setNormalCompletion();
+        return true;
+    }
+
+    /**
+     * Main execution method used by worker threads. Invokes
+     * base computation unless already complete.
+     */
+    final void quietlyExec() {
+        if (status >= 0) {
+            try {
+                if (!exec())
+                    return;
+            } catch (Throwable rex) {
+                setDoneExceptionally(rex);
+                return;
+            }
+            setNormalCompletion();
+        }
+    }
+
+    /**
+     * Calls exec(), recording but not rethrowing exception.
+     * Caller should normally check status before calling.
+     *
+     * @return true if completed normally
+     */
+    private boolean tryQuietlyInvoke() {
+        try {
+            if (!exec())
+                return false;
+        } catch (Throwable rex) {
+            setDoneExceptionally(rex);
+            return false;
+        }
+        setNormalCompletion();
+        return true;
+    }
+
+    /**
+     * Cancels, ignoring any exceptions it throws.
+     */
+    final void cancelIgnoringExceptions() {
+        try {
+            cancel(false);
+        } catch (Throwable ignore) {
+        }
+    }
+
+    /**
+     * Main implementation of helpJoin
+     */
+    private int busyJoin(ForkJoinWorkerThread w) {
+        int s;
+        ForkJoinTask<?> t;
+        while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
+            t.quietlyExec();
+        return (s >= 0) ? awaitDone(w, false) : s; // block if no work
+    }
+
+    // public methods
+
+    /**
+     * Arranges to asynchronously execute this task.  While it is not
+     * necessarily enforced, it is a usage error to fork a task more
+     * than once unless it has completed and been reinitialized.
+     * Subsequent modifications to the state of this task or any data
+     * it operates on are not necessarily consistently observable by
+     * any thread other than the one executing it unless preceded by a
+     * call to {@link #join} or related methods, or a call to {@link
+     * #isDone} returning {@code true}.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return {@code this}, to simplify usage
+     */
+    public final ForkJoinTask<V> fork() {
+        ((ForkJoinWorkerThread) Thread.currentThread())
+            .pushTask(this);
+        return this;
+    }
+
+    /**
+     * Returns the result of the computation when it {@link #isDone is done}.
+     * This method differs from {@link #get()} in that
+     * abnormal completion results in {@code RuntimeException} or
+     * {@code Error}, not {@code ExecutionException}.
+     *
+     * @return the computed result
+     */
+    public final V join() {
+        ForkJoinWorkerThread w = getWorker();
+        if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
+            reportException(awaitDone(w, true));
+        return getRawResult();
+    }
+
+    /**
+     * Commences performing this task, awaits its completion if
+     * necessary, and return its result, or throws an (unchecked)
+     * exception if the underlying computation did so.
+     *
+     * @return the computed result
+     */
+    public final V invoke() {
+        if (status >= 0 && tryExec())
+            return getRawResult();
+        else
+            return join();
+    }
+
+    /**
+     * Forks the given tasks, returning when {@code isDone} holds for
+     * each task or an (unchecked) exception is encountered, in which
+     * case the exception is rethrown.  If either task encounters an
+     * exception, the other one may be, but is not guaranteed to be,
+     * cancelled.  If both tasks throw an exception, then this method
+     * throws one of them.  The individual status of each task may be
+     * checked using {@link #getException()} and related methods.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @param t1 the first task
+     * @param t2 the second task
+     * @throws NullPointerException if any task is null
+     */
+    public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
+        t2.fork();
+        t1.invoke();
+        t2.join();
+    }
+
+    /**
+     * Forks the given tasks, returning when {@code isDone} holds for
+     * each task or an (unchecked) exception is encountered, in which
+     * case the exception is rethrown. If any task encounters an
+     * exception, others may be, but are not guaranteed to be,
+     * cancelled.  If more than one task encounters an exception, then
+     * this method throws any one of these exceptions.  The individual
+     * status of each task may be checked using {@link #getException()}
+     * and related methods.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @param tasks the tasks
+     * @throws NullPointerException if any task is null
+     */
+    public static void invokeAll(ForkJoinTask<?>... tasks) {
+        Throwable ex = null;
+        int last = tasks.length - 1;
+        for (int i = last; i >= 0; --i) {
+            ForkJoinTask<?> t = tasks[i];
+            if (t == null) {
+                if (ex == null)
+                    ex = new NullPointerException();
+            }
+            else if (i != 0)
+                t.fork();
+            else {
+                t.quietlyInvoke();
+                if (ex == null)
+                    ex = t.getException();
+            }
+        }
+        for (int i = 1; i <= last; ++i) {
+            ForkJoinTask<?> t = tasks[i];
+            if (t != null) {
+                if (ex != null)
+                    t.cancel(false);
+                else {
+                    t.quietlyJoin();
+                    if (ex == null)
+                        ex = t.getException();
+                }
+            }
+        }
+        if (ex != null)
+            rethrowException(ex);
+    }
+
+    /**
+     * Forks all tasks in the specified collection, returning when
+     * {@code isDone} holds for each task or an (unchecked) exception
+     * is encountered.  If any task encounters an exception, others
+     * may be, but are not guaranteed to be, cancelled.  If more than
+     * one task encounters an exception, then this method throws any
+     * one of these exceptions.  The individual status of each task
+     * may be checked using {@link #getException()} and related
+     * methods.  The behavior of this operation is undefined if the
+     * specified collection is modified while the operation is in
+     * progress.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @param tasks the collection of tasks
+     * @return the tasks argument, to simplify usage
+     * @throws NullPointerException if tasks or any element are null
+     */
+    public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
+        if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
+            invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
+            return tasks;
+        }
+        @SuppressWarnings("unchecked")
+        List<? extends ForkJoinTask<?>> ts =
+            (List<? extends ForkJoinTask<?>>) tasks;
+        Throwable ex = null;
+        int last = ts.size() - 1;
+        for (int i = last; i >= 0; --i) {
+            ForkJoinTask<?> t = ts.get(i);
+            if (t == null) {
+                if (ex == null)
+                    ex = new NullPointerException();
+            }
+            else if (i != 0)
+                t.fork();
+            else {
+                t.quietlyInvoke();
+                if (ex == null)
+                    ex = t.getException();
+            }
+        }
+        for (int i = 1; i <= last; ++i) {
+            ForkJoinTask<?> t = ts.get(i);
+            if (t != null) {
+                if (ex != null)
+                    t.cancel(false);
+                else {
+                    t.quietlyJoin();
+                    if (ex == null)
+                        ex = t.getException();
+                }
+            }
+        }
+        if (ex != null)
+            rethrowException(ex);
+        return tasks;
+    }
+
+    /**
+     * Attempts to cancel execution of this task. This attempt will
+     * fail if the task has already completed, has already been
+     * cancelled, or could not be cancelled for some other reason. If
+     * successful, and this task has not started when cancel is
+     * called, execution of this task is suppressed, {@link
+     * #isCancelled} will report true, and {@link #join} will result
+     * in a {@code CancellationException} being thrown.
+     *
+     * <p>This method may be overridden in subclasses, but if so, must
+     * still ensure that these minimal properties hold. In particular,
+     * the {@code cancel} method itself must not throw exceptions.
+     *
+     * <p>This method is designed to be invoked by <em>other</em>
+     * tasks. To terminate the current task, you can just return or
+     * throw an unchecked exception from its computation method, or
+     * invoke {@link #completeExceptionally}.
+     *
+     * @param mayInterruptIfRunning this value is ignored in the
+     * default implementation because tasks are not
+     * cancelled via interruption
+     *
+     * @return {@code true} if this task is now cancelled
+     */
+    public boolean cancel(boolean mayInterruptIfRunning) {
+        setCompletion(CANCELLED);
+        return (status & COMPLETION_MASK) == CANCELLED;
+    }
+
+    public final boolean isDone() {
+        return status < 0;
+    }
+
+    public final boolean isCancelled() {
+        return (status & COMPLETION_MASK) == CANCELLED;
+    }
+
+    /**
+     * Returns {@code true} if this task threw an exception or was cancelled.
+     *
+     * @return {@code true} if this task threw an exception or was cancelled
+     */
+    public final boolean isCompletedAbnormally() {
+        return (status & COMPLETION_MASK) < NORMAL;
+    }
+
+    /**
+     * Returns {@code true} if this task completed without throwing an
+     * exception and was not cancelled.
+     *
+     * @return {@code true} if this task completed without throwing an
+     * exception and was not cancelled
+     */
+    public final boolean isCompletedNormally() {
+        return (status & COMPLETION_MASK) == NORMAL;
+    }
+
+    /**
+     * Returns the exception thrown by the base computation, or a
+     * {@code CancellationException} if cancelled, or {@code null} if
+     * none or if the method has not yet completed.
+     *
+     * @return the exception, or {@code null} if none
+     */
+    public final Throwable getException() {
+        int s = status & COMPLETION_MASK;
+        return ((s >= NORMAL)    ? null :
+                (s == CANCELLED) ? new CancellationException() :
+                exceptionMap.get(this));
+    }
+
+    /**
+     * Completes this task abnormally, and if not already aborted or
+     * cancelled, causes it to throw the given exception upon
+     * {@code join} and related operations. This method may be used
+     * to induce exceptions in asynchronous tasks, or to force
+     * completion of tasks that would not otherwise complete.  Its use
+     * in other situations is discouraged.  This method is
+     * overridable, but overridden versions must invoke {@code super}
+     * implementation to maintain guarantees.
+     *
+     * @param ex the exception to throw. If this exception is not a
+     * {@code RuntimeException} or {@code Error}, the actual exception
+     * thrown will be a {@code RuntimeException} with cause {@code ex}.
+     */
+    public void completeExceptionally(Throwable ex) {
+        setDoneExceptionally((ex instanceof RuntimeException) ||
+                             (ex instanceof Error) ? ex :
+                             new RuntimeException(ex));
+    }
+
+    /**
+     * Completes this task, and if not already aborted or cancelled,
+     * returning a {@code null} result upon {@code join} and related
+     * operations. This method may be used to provide results for
+     * asynchronous tasks, or to provide alternative handling for
+     * tasks that would not otherwise complete normally. Its use in
+     * other situations is discouraged. This method is
+     * overridable, but overridden versions must invoke {@code super}
+     * implementation to maintain guarantees.
+     *
+     * @param value the result value for this task
+     */
+    public void complete(V value) {
+        try {
+            setRawResult(value);
+        } catch (Throwable rex) {
+            setDoneExceptionally(rex);
+            return;
+        }
+        setNormalCompletion();
+    }
+
+    public final V get() throws InterruptedException, ExecutionException {
+        ForkJoinWorkerThread w = getWorker();
+        if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
+            awaitDone(w, true);
+        return reportFutureResult();
+    }
+
+    public final V get(long timeout, TimeUnit unit)
+        throws InterruptedException, ExecutionException, TimeoutException {
+        long nanos = unit.toNanos(timeout);
+        ForkJoinWorkerThread w = getWorker();
+        if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
+            awaitDone(w, nanos);
+        return reportTimedFutureResult();
+    }
+
+    /**
+     * Possibly executes other tasks until this task {@link #isDone is
+     * done}, then returns the result of the computation.  This method
+     * may be more efficient than {@code join}, but is only applicable
+     * when there are no potential dependencies between continuation
+     * of the current task and that of any other task that might be
+     * executed while helping. (This usually holds for pure
+     * divide-and-conquer tasks).
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return the computed result
+     */
+    public final V helpJoin() {
+        ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
+        if (status < 0 || !w.unpushTask(this) || !tryExec())
+            reportException(busyJoin(w));
+        return getRawResult();
+    }
+
+    /**
+     * Possibly executes other tasks until this task {@link #isDone is
+     * done}.  This method may be useful when processing collections
+     * of tasks when some have been cancelled or otherwise known to
+     * have aborted.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     */
+    public final void quietlyHelpJoin() {
+        if (status >= 0) {
+            ForkJoinWorkerThread w =
+                (ForkJoinWorkerThread) Thread.currentThread();
+            if (!w.unpushTask(this) || !tryQuietlyInvoke())
+                busyJoin(w);
+        }
+    }
+
+    /**
+     * Joins this task, without returning its result or throwing an
+     * exception. This method may be useful when processing
+     * collections of tasks when some have been cancelled or otherwise
+     * known to have aborted.
+     */
+    public final void quietlyJoin() {
+        if (status >= 0) {
+            ForkJoinWorkerThread w = getWorker();
+            if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
+                awaitDone(w, true);
+        }
+    }
+
+    /**
+     * Commences performing this task and awaits its completion if
+     * necessary, without returning its result or throwing an
+     * exception. This method may be useful when processing
+     * collections of tasks when some have been cancelled or otherwise
+     * known to have aborted.
+     */
+    public final void quietlyInvoke() {
+        if (status >= 0 && !tryQuietlyInvoke())
+            quietlyJoin();
+    }
+
+    /**
+     * Possibly executes tasks until the pool hosting the current task
+     * {@link ForkJoinPool#isQuiescent is quiescent}. This method may
+     * be of use in designs in which many tasks are forked, but none
+     * are explicitly joined, instead executing them until all are
+     * processed.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     */
+    public static void helpQuiesce() {
+        ((ForkJoinWorkerThread) Thread.currentThread())
+            .helpQuiescePool();
+    }
+
+    /**
+     * Resets the internal bookkeeping state of this task, allowing a
+     * subsequent {@code fork}. This method allows repeated reuse of
+     * this task, but only if reuse occurs when this task has either
+     * never been forked, or has been forked, then completed and all
+     * outstanding joins of this task have also completed. Effects
+     * under any other usage conditions are not guaranteed.
+     * This method may be useful when executing
+     * pre-constructed trees of subtasks in loops.
+     */
+    public void reinitialize() {
+        if ((status & COMPLETION_MASK) == EXCEPTIONAL)
+            exceptionMap.remove(this);
+        status = 0;
+    }
+
+    /**
+     * Returns the pool hosting the current task execution, or null
+     * if this task is executing outside of any ForkJoinPool.
+     *
+     * @see #inForkJoinPool
+     * @return the pool, or {@code null} if none
+     */
+    public static ForkJoinPool getPool() {
+        Thread t = Thread.currentThread();
+        return (t instanceof ForkJoinWorkerThread) ?
+            ((ForkJoinWorkerThread) t).pool : null;
+    }
+
+    /**
+     * Returns {@code true} if the current thread is executing as a
+     * ForkJoinPool computation.
+     *
+     * @return {@code true} if the current thread is executing as a
+     * ForkJoinPool computation, or false otherwise
+     */
+    public static boolean inForkJoinPool() {
+        return Thread.currentThread() instanceof ForkJoinWorkerThread;
+    }
+
+    /**
+     * Tries to unschedule this task for execution. This method will
+     * typically succeed if this task is the most recently forked task
+     * by the current thread, and has not commenced executing in
+     * another thread.  This method may be useful when arranging
+     * alternative local processing of tasks that could have been, but
+     * were not, stolen.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return {@code true} if unforked
+     */
+    public boolean tryUnfork() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .unpushTask(this);
+    }
+
+    /**
+     * Returns an estimate of the number of tasks that have been
+     * forked by the current worker thread but not yet executed. This
+     * value may be useful for heuristic decisions about whether to
+     * fork other tasks.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return the number of tasks
+     */
+    public static int getQueuedTaskCount() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .getQueueSize();
+    }
+
+    /**
+     * Returns an estimate of how many more locally queued tasks are
+     * held by the current worker thread than there are other worker
+     * threads that might steal them.  This value may be useful for
+     * heuristic decisions about whether to fork other tasks. In many
+     * usages of ForkJoinTasks, at steady state, each worker should
+     * aim to maintain a small constant surplus (for example, 3) of
+     * tasks, and to process computations locally if this threshold is
+     * exceeded.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return the surplus number of tasks, which may be negative
+     */
+    public static int getSurplusQueuedTaskCount() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .getEstimatedSurplusTaskCount();
+    }
+
+    // Extension methods
+
+    /**
+     * Returns the result that would be returned by {@link #join}, even
+     * if this task completed abnormally, or {@code null} if this task
+     * is not known to have been completed.  This method is designed
+     * to aid debugging, as well as to support extensions. Its use in
+     * any other context is discouraged.
+     *
+     * @return the result, or {@code null} if not completed
+     */
+    public abstract V getRawResult();
+
+    /**
+     * Forces the given value to be returned as a result.  This method
+     * is designed to support extensions, and should not in general be
+     * called otherwise.
+     *
+     * @param value the value
+     */
+    protected abstract void setRawResult(V value);
+
+    /**
+     * Immediately performs the base action of this task.  This method
+     * is designed to support extensions, and should not in general be
+     * called otherwise. The return value controls whether this task
+     * is considered to be done normally. It may return false in
+     * asynchronous actions that require explicit invocations of
+     * {@link #complete} to become joinable. It may also throw an
+     * (unchecked) exception to indicate abnormal exit.
+     *
+     * @return {@code true} if completed normally
+     */
+    protected abstract boolean exec();
+
+    /**
+     * Returns, but does not unschedule or execute, a task queued by
+     * the current thread but not yet executed, if one is immediately
+     * available. There is no guarantee that this task will actually
+     * be polled or executed next. Conversely, this method may return
+     * null even if a task exists but cannot be accessed without
+     * contention with other threads.  This method is designed
+     * primarily to support extensions, and is unlikely to be useful
+     * otherwise.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return the next task, or {@code null} if none are available
+     */
+    protected static ForkJoinTask<?> peekNextLocalTask() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .peekTask();
+    }
+
+    /**
+     * Unschedules and returns, without executing, the next task
+     * queued by the current thread but not yet executed.  This method
+     * is designed primarily to support extensions, and is unlikely to
+     * be useful otherwise.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return the next task, or {@code null} if none are available
+     */
+    protected static ForkJoinTask<?> pollNextLocalTask() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .pollLocalTask();
+    }
+
+    /**
+     * Unschedules and returns, without executing, the next task
+     * queued by the current thread but not yet executed, if one is
+     * available, or if not available, a task that was forked by some
+     * other thread, if available. Availability may be transient, so a
+     * {@code null} result does not necessarily imply quiescence
+     * of the pool this task is operating in.  This method is designed
+     * primarily to support extensions, and is unlikely to be useful
+     * otherwise.
+     *
+     * <p>This method may be invoked only from within {@code
+     * ForkJoinTask} computations (as may be determined using method
+     * {@link #inForkJoinPool}).  Attempts to invoke in other contexts
+     * result in exceptions or errors, possibly including {@code
+     * ClassCastException}.
+     *
+     * @return a task, or {@code null} if none are available
+     */
+    protected static ForkJoinTask<?> pollTask() {
+        return ((ForkJoinWorkerThread) Thread.currentThread())
+            .pollTask();
+    }
+
+    /**
+     * Adaptor for Runnables. This implements RunnableFuture
+     * to be compliant with AbstractExecutorService constraints
+     * when used in ForkJoinPool.
+     */
+    static final class AdaptedRunnable<T> extends ForkJoinTask<T>
+        implements RunnableFuture<T> {
+        final Runnable runnable;
+        final T resultOnCompletion;
+        T result;
+        AdaptedRunnable(Runnable runnable, T result) {
+            if (runnable == null) throw new NullPointerException();
+            this.runnable = runnable;
+            this.resultOnCompletion = result;
+        }
+        public T getRawResult() { return result; }
+        public void setRawResult(T v) { result = v; }
+        public boolean exec() {
+            runnable.run();
+            result = resultOnCompletion;
+            return true;
+        }
+        public void run() { invoke(); }
+        private static final long serialVersionUID = 5232453952276885070L;
+    }
+
+    /**
+     * Adaptor for Callables
+     */
+    static final class AdaptedCallable<T> extends ForkJoinTask<T>
+        implements RunnableFuture<T> {
+        final Callable<? extends T> callable;
+        T result;
+        AdaptedCallable(Callable<? extends T> callable) {
+            if (callable == null) throw new NullPointerException();
+            this.callable = callable;
+        }
+        public T getRawResult() { return result; }
+        public void setRawResult(T v) { result = v; }
+        public boolean exec() {
+            try {
+                result = callable.call();
+                return true;
+            } catch (Error err) {
+                throw err;
+            } catch (RuntimeException rex) {
+                throw rex;
+            } catch (Exception ex) {
+                throw new RuntimeException(ex);
+            }
+        }
+        public void run() { invoke(); }
+        private static final long serialVersionUID = 2838392045355241008L;
+    }
+
+    /**
+     * Returns a new {@code ForkJoinTask} that performs the {@code run}
+     * method of the given {@code Runnable} as its action, and returns
+     * a null result upon {@link #join}.
+     *
+     * @param runnable the runnable action
+     * @return the task
+     */
+    public static ForkJoinTask<?> adapt(Runnable runnable) {
+        return new AdaptedRunnable<Void>(runnable, null);
+    }
+
+    /**
+     * Returns a new {@code ForkJoinTask} that performs the {@code run}
+     * method of the given {@code Runnable} as its action, and returns
+     * the given result upon {@link #join}.
+     *
+     * @param runnable the runnable action
+     * @param result the result upon completion
+     * @return the task
+     */
+    public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
+        return new AdaptedRunnable<T>(runnable, result);
+    }
+
+    /**
+     * Returns a new {@code ForkJoinTask} that performs the {@code call}
+     * method of the given {@code Callable} as its action, and returns
+     * its result upon {@link #join}, translating any checked exceptions
+     * encountered into {@code RuntimeException}.
+     *
+     * @param callable the callable action
+     * @return the task
+     */
+    public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
+        return new AdaptedCallable<T>(callable);
+    }
+
+    // Serialization support
+
+    private static final long serialVersionUID = -7721805057305804111L;
+
+    /**
+     * Saves the state to a stream.
+     *
+     * @serialData the current run status and the exception thrown
+     * during execution, or {@code null} if none
+     * @param s the stream
+     */
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+        s.defaultWriteObject();
+        s.writeObject(getException());
+    }
+
+    /**
+     * Reconstitutes the instance from a stream.
+     *
+     * @param s the stream
+     */
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        s.defaultReadObject();
+        status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
+        status |= EXTERNAL_SIGNAL; // conservatively set external signal
+        Object ex = s.readObject();
+        if (ex != null)
+            setDoneExceptionally((Throwable) ex);
+    }
+
+    // Unsafe mechanics
+
+    private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+    private static final long statusOffset =
+        objectFieldOffset("status", ForkJoinTask.class);
+
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to corresponding Error
+            NoSuchFieldError error = new NoSuchFieldError(field);
+            error.initCause(e);
+            throw error;
+        }
+    }
+}

src/share/classes/java/util/concurrent/ForkJoinWorkerThread.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.util.Collection;
+
+/**
+ * A thread managed by a {@link ForkJoinPool}.  This class is
+ * subclassable solely for the sake of adding functionality -- there
+ * are no overridable methods dealing with scheduling or execution.
+ * However, you can override initialization and termination methods
+ * surrounding the main task processing loop.  If you do create such a
+ * subclass, you will also need to supply a custom {@link
+ * ForkJoinPool.ForkJoinWorkerThreadFactory} to use it in a {@code
+ * ForkJoinPool}.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ForkJoinWorkerThread extends Thread {
+    /*
+     * Algorithm overview:
+     *
+     * 1. Work-Stealing: Work-stealing queues are special forms of
+     * Deques that support only three of the four possible
+     * end-operations -- push, pop, and deq (aka steal), and only do
+     * so under the constraints that push and pop are called only from
+     * the owning thread, while deq may be called from other threads.
+     * (If you are unfamiliar with them, you probably want to read
+     * Herlihy and Shavit's book "The Art of Multiprocessor
+     * programming", chapter 16 describing these in more detail before
+     * proceeding.)  The main work-stealing queue design is roughly
+     * similar to "Dynamic Circular Work-Stealing Deque" by David
+     * Chase and Yossi Lev, SPAA 2005
+     * (http://research.sun.com/scalable/pubs/index.html).  The main
+     * difference ultimately stems from gc requirements that we null
+     * out taken slots as soon as we can, to maintain as small a
+     * footprint as possible even in programs generating huge numbers
+     * of tasks. To accomplish this, we shift the CAS arbitrating pop
+     * vs deq (steal) from being on the indices ("base" and "sp") to
+     * the slots themselves (mainly via method "casSlotNull()"). So,
+     * both a successful pop and deq mainly entail CAS'ing a non-null
+     * slot to null.  Because we rely on CASes of references, we do
+     * not need tag bits on base or sp.  They are simple ints as used
+     * in any circular array-based queue (see for example ArrayDeque).
+     * Updates to the indices must still be ordered in a way that
+     * guarantees that (sp - base) > 0 means the queue is empty, but
+     * otherwise may err on the side of possibly making the queue
+     * appear nonempty when a push, pop, or deq have not fully
+     * committed. Note that this means that the deq operation,
+     * considered individually, is not wait-free. One thief cannot
+     * successfully continue until another in-progress one (or, if
+     * previously empty, a push) completes.  However, in the
+     * aggregate, we ensure at least probabilistic
+     * non-blockingness. If an attempted steal fails, a thief always
+     * chooses a different random victim target to try next. So, in
+     * order for one thief to progress, it suffices for any
+     * in-progress deq or new push on any empty queue to complete. One
+     * reason this works well here is that apparently-nonempty often
+     * means soon-to-be-stealable, which gives threads a chance to
+     * activate if necessary before stealing (see below).
+     *
+     * This approach also enables support for "async mode" where local
+     * task processing is in FIFO, not LIFO order; simply by using a
+     * version of deq rather than pop when locallyFifo is true (as set
+     * by the ForkJoinPool).  This allows use in message-passing
+     * frameworks in which tasks are never joined.
+     *
+     * Efficient implementation of this approach currently relies on
+     * an uncomfortable amount of "Unsafe" mechanics. To maintain
+     * correct orderings, reads and writes of variable base require
+     * volatile ordering.  Variable sp does not require volatile write
+     * but needs cheaper store-ordering on writes.  Because they are
+     * protected by volatile base reads, reads of the queue array and
+     * its slots do not need volatile load semantics, but writes (in
+     * push) require store order and CASes (in pop and deq) require
+     * (volatile) CAS semantics.  (See "Idempotent work stealing" by
+     * Michael, Saraswat, and Vechev, PPoPP 2009
+     * http://portal.acm.org/citation.cfm?id=1504186 for an algorithm
+     * with similar properties, but without support for nulling
+     * slots.)  Since these combinations aren't supported using
+     * ordinary volatiles, the only way to accomplish these
+     * efficiently is to use direct Unsafe calls. (Using external
+     * AtomicIntegers and AtomicReferenceArrays for the indices and
+     * array is significantly slower because of memory locality and
+     * indirection effects.)
+     *
+     * Further, performance on most platforms is very sensitive to
+     * placement and sizing of the (resizable) queue array.  Even
+     * though these queues don't usually become all that big, the
+     * initial size must be large enough to counteract cache
+     * contention effects across multiple queues (especially in the
+     * presence of GC cardmarking). Also, to improve thread-locality,
+     * queues are currently initialized immediately after the thread
+     * gets the initial signal to start processing tasks.  However,
+     * all queue-related methods except pushTask are written in a way
+     * that allows them to instead be lazily allocated and/or disposed
+     * of when empty. All together, these low-level implementation
+     * choices produce as much as a factor of 4 performance
+     * improvement compared to naive implementations, and enable the
+     * processing of billions of tasks per second, sometimes at the
+     * expense of ugliness.
+     *
+     * 2. Run control: The primary run control is based on a global
+     * counter (activeCount) held by the pool. It uses an algorithm
+     * similar to that in Herlihy and Shavit section 17.6 to cause
+     * threads to eventually block when all threads declare they are
+     * inactive. For this to work, threads must be declared active
+     * when executing tasks, and before stealing a task. They must be
+     * inactive before blocking on the Pool Barrier (awaiting a new
+     * submission or other Pool event). In between, there is some free
+     * play which we take advantage of to avoid contention and rapid
+     * flickering of the global activeCount: If inactive, we activate
+     * only if a victim queue appears to be nonempty (see above).
+     * Similarly, a thread tries to inactivate only after a full scan
+     * of other threads.  The net effect is that contention on
+     * activeCount is rarely a measurable performance issue. (There
+     * are also a few other cases where we scan for work rather than
+     * retry/block upon contention.)
+     *
+     * 3. Selection control. We maintain policy of always choosing to
+     * run local tasks rather than stealing, and always trying to
+     * steal tasks before trying to run a new submission. All steals
+     * are currently performed in randomly-chosen deq-order. It may be
+     * worthwhile to bias these with locality / anti-locality
+     * information, but doing this well probably requires more
+     * lower-level information from JVMs than currently provided.
+     */
+
+    /**
+     * Capacity of work-stealing queue array upon initialization.
+     * Must be a power of two. Initial size must be at least 2, but is
+     * padded to minimize cache effects.
+     */
+    private static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
+
+    /**
+     * Maximum work-stealing queue array size.  Must be less than or
+     * equal to 1 << 28 to ensure lack of index wraparound. (This
+     * is less than usual bounds, because we need leftshift by 3
+     * to be in int range).
+     */
+    private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
+
+    /**
+     * The pool this thread works in. Accessed directly by ForkJoinTask.
+     */
+    final ForkJoinPool pool;
+
+    /**
+     * The work-stealing queue array. Size must be a power of two.
+     * Initialized when thread starts, to improve memory locality.
+     */
+    private ForkJoinTask<?>[] queue;
+
+    /**
+     * Index (mod queue.length) of next queue slot to push to or pop
+     * from. It is written only by owner thread, via ordered store.
+     * Both sp and base are allowed to wrap around on overflow, but
+     * (sp - base) still estimates size.
+     */
+    private volatile int sp;
+
+    /**
+     * Index (mod queue.length) of least valid queue slot, which is
+     * always the next position to steal from if nonempty.
+     */
+    private volatile int base;
+
+    /**
+     * Activity status. When true, this worker is considered active.
+     * Must be false upon construction. It must be true when executing
+     * tasks, and BEFORE stealing a task. It must be false before
+     * calling pool.sync.
+     */
+    private boolean active;
+
+    /**
+     * Run state of this worker. Supports simple versions of the usual
+     * shutdown/shutdownNow control.
+     */
+    private volatile int runState;
+
+    /**
+     * Seed for random number generator for choosing steal victims.
+     * Uses Marsaglia xorshift. Must be nonzero upon initialization.
+     */
+    private int seed;
+
+    /**
+     * Number of steals, transferred to pool when idle
+     */
+    private int stealCount;
+
+    /**
+     * Index of this worker in pool array. Set once by pool before
+     * running, and accessed directly by pool during cleanup etc.
+     */
+    int poolIndex;
+
+    /**
+     * The last barrier event waited for. Accessed in pool callback
+     * methods, but only by current thread.
+     */
+    long lastEventCount;
+
+    /**
+     * True if use local fifo, not default lifo, for local polling
+     */
+    private boolean locallyFifo;
+
+    /**
+     * Creates a ForkJoinWorkerThread operating in the given pool.
+     *
+     * @param pool the pool this thread works in
+     * @throws NullPointerException if pool is null
+     */
+    protected ForkJoinWorkerThread(ForkJoinPool pool) {
+        if (pool == null) throw new NullPointerException();
+        this.pool = pool;
+        // Note: poolIndex is set by pool during construction
+        // Remaining initialization is deferred to onStart
+    }
+
+    // Public access methods
+
+    /**
+     * Returns the pool hosting this thread.
+     *
+     * @return the pool
+     */
+    public ForkJoinPool getPool() {
+        return pool;
+    }
+
+    /**
+     * Returns the index number of this thread in its pool.  The
+     * returned value ranges from zero to the maximum number of
+     * threads (minus one) that have ever been created in the pool.
+     * This method may be useful for applications that track status or
+     * collect results per-worker rather than per-task.
+     *
+     * @return the index number
+     */
+    public int getPoolIndex() {
+        return poolIndex;
+    }
+
+    /**
+     * Establishes local first-in-first-out scheduling mode for forked
+     * tasks that are never joined.
+     *
+     * @param async if true, use locally FIFO scheduling
+     */
+    void setAsyncMode(boolean async) {
+        locallyFifo = async;
+    }
+
+    // Runstate management
+
+    // Runstate values. Order matters
+    private static final int RUNNING     = 0;
+    private static final int SHUTDOWN    = 1;
+    private static final int TERMINATING = 2;
+    private static final int TERMINATED  = 3;
+
+    final boolean isShutdown()    { return runState >= SHUTDOWN;  }
+    final boolean isTerminating() { return runState >= TERMINATING;  }
+    final boolean isTerminated()  { return runState == TERMINATED; }
+    final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
+    final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
+
+    /**
+     * Transitions to at least the given state.
+     *
+     * @return {@code true} if not already at least at given state
+     */
+    private boolean transitionRunStateTo(int state) {
+        for (;;) {
+            int s = runState;
+            if (s >= state)
+                return false;
+            if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
+                return true;
+        }
+    }
+
+    /**
+     * Tries to set status to active; fails on contention.
+     */
+    private boolean tryActivate() {
+        if (!active) {
+            if (!pool.tryIncrementActiveCount())
+                return false;
+            active = true;
+        }
+        return true;
+    }
+
+    /**
+     * Tries to set status to inactive; fails on contention.
+     */
+    private boolean tryInactivate() {
+        if (active) {
+            if (!pool.tryDecrementActiveCount())
+                return false;
+            active = false;
+        }
+        return true;
+    }
+
+    /**
+     * Computes next value for random victim probe.  Scans don't
+     * require a very high quality generator, but also not a crummy
+     * one.  Marsaglia xor-shift is cheap and works well.
+     */
+    private static int xorShift(int r) {
+        r ^= (r << 13);
+        r ^= (r >>> 17);
+        return r ^ (r << 5);
+    }
+
+    // Lifecycle methods
+
+    /**
+     * This method is required to be public, but should never be
+     * called explicitly. It performs the main run loop to execute
+     * ForkJoinTasks.
+     */
+    public void run() {
+        Throwable exception = null;
+        try {
+            onStart();
+            pool.sync(this); // await first pool event
+            mainLoop();
+        } catch (Throwable ex) {
+            exception = ex;
+        } finally {
+            onTermination(exception);
+        }
+    }
+
+    /**
+     * Executes tasks until shut down.
+     */
+    private void mainLoop() {
+        while (!isShutdown()) {
+            ForkJoinTask<?> t = pollTask();
+            if (t != null || (t = pollSubmission()) != null)
+                t.quietlyExec();
+            else if (tryInactivate())
+                pool.sync(this);
+        }
+    }
+
+    /**
+     * Initializes internal state after construction but before
+     * processing any tasks. If you override this method, you must
+     * invoke super.onStart() at the beginning of the method.
+     * Initialization requires care: Most fields must have legal
+     * default values, to ensure that attempted accesses from other
+     * threads work correctly even before this thread starts
+     * processing tasks.
+     */
+    protected void onStart() {
+        // Allocate while starting to improve chances of thread-local
+        // isolation
+        queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
+        // Initial value of seed need not be especially random but
+        // should differ across workers and must be nonzero
+        int p = poolIndex + 1;
+        seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
+    }
+
+    /**
+     * Performs cleanup associated with termination of this worker
+     * thread.  If you override this method, you must invoke
+     * {@code super.onTermination} at the end of the overridden method.
+     *
+     * @param exception the exception causing this thread to abort due
+     * to an unrecoverable error, or {@code null} if completed normally
+     */
+    protected void onTermination(Throwable exception) {
+        // Execute remaining local tasks unless aborting or terminating
+        while (exception == null && pool.isProcessingTasks() && base != sp) {
+            try {
+                ForkJoinTask<?> t = popTask();
+                if (t != null)
+                    t.quietlyExec();
+            } catch (Throwable ex) {
+                exception = ex;
+            }
+        }
+        // Cancel other tasks, transition status, notify pool, and
+        // propagate exception to uncaught exception handler
+        try {
+            do {} while (!tryInactivate()); // ensure inactive
+            cancelTasks();
+            runState = TERMINATED;
+            pool.workerTerminated(this);
+        } catch (Throwable ex) {        // Shouldn't ever happen
+            if (exception == null)      // but if so, at least rethrown
+                exception = ex;
+        } finally {
+            if (exception != null)
+                ForkJoinTask.rethrowException(exception);
+        }
+    }
+
+    // Intrinsics-based support for queue operations.
+
+    private static long slotOffset(int i) {
+        return ((long) i << qShift) + qBase;
+    }
+
+    /**
+     * Adds in store-order the given task at given slot of q to null.
+     * Caller must ensure q is non-null and index is in range.
+     */
+    private static void setSlot(ForkJoinTask<?>[] q, int i,
+                                ForkJoinTask<?> t) {
+        UNSAFE.putOrderedObject(q, slotOffset(i), t);
+    }
+
+    /**
+     * CAS given slot of q to null. Caller must ensure q is non-null
+     * and index is in range.
+     */
+    private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
+                                       ForkJoinTask<?> t) {
+        return UNSAFE.compareAndSwapObject(q, slotOffset(i), t, null);
+    }
+
+    /**
+     * Sets sp in store-order.
+     */
+    private void storeSp(int s) {
+        UNSAFE.putOrderedInt(this, spOffset, s);
+    }
+
+    // Main queue methods
+
+    /**
+     * Pushes a task. Called only by current thread.
+     *
+     * @param t the task. Caller must ensure non-null.
+     */
+    final void pushTask(ForkJoinTask<?> t) {
+        ForkJoinTask<?>[] q = queue;
+        int mask = q.length - 1;
+        int s = sp;
+        setSlot(q, s & mask, t);
+        storeSp(++s);
+        if ((s -= base) == 1)
+            pool.signalWork();
+        else if (s >= mask)
+            growQueue();
+    }
+
+    /**
+     * Tries to take a task from the base of the queue, failing if
+     * either empty or contended.
+     *
+     * @return a task, or null if none or contended
+     */
+    final ForkJoinTask<?> deqTask() {
+        ForkJoinTask<?> t;
+        ForkJoinTask<?>[] q;
+        int i;
+        int b;
+        if (sp != (b = base) &&
+            (q = queue) != null && // must read q after b
+            (t = q[i = (q.length - 1) & b]) != null &&
+            casSlotNull(q, i, t)) {
+            base = b + 1;
+            return t;
+        }
+        return null;
+    }
+
+    /**
+     * Tries to take a task from the base of own queue, activating if
+     * necessary, failing only if empty. Called only by current thread.
+     *
+     * @return a task, or null if none
+     */
+    final ForkJoinTask<?> locallyDeqTask() {
+        int b;
+        while (sp != (b = base)) {
+            if (tryActivate()) {
+                ForkJoinTask<?>[] q = queue;
+                int i = (q.length - 1) & b;
+                ForkJoinTask<?> t = q[i];
+                if (t != null && casSlotNull(q, i, t)) {
+                    base = b + 1;
+                    return t;
+                }
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns a popped task, or null if empty. Ensures active status
+     * if non-null. Called only by current thread.
+     */
+    final ForkJoinTask<?> popTask() {
+        int s = sp;
+        while (s != base) {
+            if (tryActivate()) {
+                ForkJoinTask<?>[] q = queue;
+                int mask = q.length - 1;
+                int i = (s - 1) & mask;
+                ForkJoinTask<?> t = q[i];
+                if (t == null || !casSlotNull(q, i, t))
+                    break;
+                storeSp(s - 1);
+                return t;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Specialized version of popTask to pop only if
+     * topmost element is the given task. Called only
+     * by current thread while active.
+     *
+     * @param t the task. Caller must ensure non-null.
+     */
+    final boolean unpushTask(ForkJoinTask<?> t) {
+        ForkJoinTask<?>[] q = queue;
+        int mask = q.length - 1;
+        int s = sp - 1;
+        if (casSlotNull(q, s & mask, t)) {
+            storeSp(s);
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * Returns next task or null if empty or contended
+     */
+    final ForkJoinTask<?> peekTask() {
+        ForkJoinTask<?>[] q = queue;
+        if (q == null)
+            return null;
+        int mask = q.length - 1;
+        int i = locallyFifo ? base : (sp - 1);
+        return q[i & mask];
+    }
+
+    /**
+     * Doubles queue array size. Transfers elements by emulating
+     * steals (deqs) from old array and placing, oldest first, into
+     * new array.
+     */
+    private void growQueue() {
+        ForkJoinTask<?>[] oldQ = queue;
+        int oldSize = oldQ.length;
+        int newSize = oldSize << 1;
+        if (newSize > MAXIMUM_QUEUE_CAPACITY)
+            throw new RejectedExecutionException("Queue capacity exceeded");
+        ForkJoinTask<?>[] newQ = queue = new ForkJoinTask<?>[newSize];
+
+        int b = base;
+        int bf = b + oldSize;
+        int oldMask = oldSize - 1;
+        int newMask = newSize - 1;
+        do {
+            int oldIndex = b & oldMask;
+            ForkJoinTask<?> t = oldQ[oldIndex];
+            if (t != null && !casSlotNull(oldQ, oldIndex, t))
+                t = null;
+            setSlot(newQ, b & newMask, t);
+        } while (++b != bf);
+        pool.signalWork();
+    }
+
+    /**
+     * Tries to steal a task from another worker. Starts at a random
+     * index of workers array, and probes workers until finding one
+     * with non-empty queue or finding that all are empty.  It
+     * randomly selects the first n probes. If these are empty, it
+     * resorts to a full circular traversal, which is necessary to
+     * accurately set active status by caller. Also restarts if pool
+     * events occurred since last scan, which forces refresh of
+     * workers array, in case barrier was associated with resize.
+     *
+     * This method must be both fast and quiet -- usually avoiding
+     * memory accesses that could disrupt cache sharing etc other than
+     * those needed to check for and take tasks. This accounts for,
+     * among other things, updating random seed in place without
+     * storing it until exit.
+     *
+     * @return a task, or null if none found
+     */
+    private ForkJoinTask<?> scan() {
+        ForkJoinTask<?> t = null;
+        int r = seed;                    // extract once to keep scan quiet
+        ForkJoinWorkerThread[] ws;       // refreshed on outer loop
+        int mask;                        // must be power 2 minus 1 and > 0
+        outer:do {
+            if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
+                int idx = r;
+                int probes = ~mask;      // use random index while negative
+                for (;;) {
+                    r = xorShift(r);     // update random seed
+                    ForkJoinWorkerThread v = ws[mask & idx];
+                    if (v == null || v.sp == v.base) {
+                        if (probes <= mask)
+                            idx = (probes++ < 0) ? r : (idx + 1);
+                        else
+                            break;
+                    }
+                    else if (!tryActivate() || (t = v.deqTask()) == null)
+                        continue outer;  // restart on contention
+                    else
+                        break outer;
+                }
+            }
+        } while (pool.hasNewSyncEvent(this)); // retry on pool events
+        seed = r;
+        return t;
+    }
+
+    /**
+     * Gets and removes a local or stolen task.
+     *
+     * @return a task, if available
+     */
+    final ForkJoinTask<?> pollTask() {
+        ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
+        if (t == null && (t = scan()) != null)
+            ++stealCount;
+        return t;
+    }
+
+    /**
+     * Gets a local task.
+     *
+     * @return a task, if available
+     */
+    final ForkJoinTask<?> pollLocalTask() {
+        return locallyFifo ? locallyDeqTask() : popTask();
+    }
+
+    /**
+     * Returns a pool submission, if one exists, activating first.
+     *
+     * @return a submission, if available
+     */
+    private ForkJoinTask<?> pollSubmission() {
+        ForkJoinPool p = pool;
+        while (p.hasQueuedSubmissions()) {
+            ForkJoinTask<?> t;
+            if (tryActivate() && (t = p.pollSubmission()) != null)
+                return t;
+        }
+        return null;
+    }
+
+    // Methods accessed only by Pool
+
+    /**
+     * Removes and cancels all tasks in queue.  Can be called from any
+     * thread.
+     */
+    final void cancelTasks() {
+        ForkJoinTask<?> t;
+        while (base != sp && (t = deqTask()) != null)
+            t.cancelIgnoringExceptions();
+    }
+
+    /**
+     * Drains tasks to given collection c.
+     *
+     * @return the number of tasks drained
+     */
+    final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
+        int n = 0;
+        ForkJoinTask<?> t;
+        while (base != sp && (t = deqTask()) != null) {
+            c.add(t);
+            ++n;
+        }
+        return n;
+    }
+
+    /**
+     * Gets and clears steal count for accumulation by pool.  Called
+     * only when known to be idle (in pool.sync and termination).
+     */
+    final int getAndClearStealCount() {
+        int sc = stealCount;
+        stealCount = 0;
+        return sc;
+    }
+
+    /**
+     * Returns {@code true} if at least one worker in the given array
+     * appears to have at least one queued task.
+     *
+     * @param ws array of workers
+     */
+    static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
+        if (ws != null) {
+            int len = ws.length;
+            for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
+                for (int i = 0; i < len; ++i) {
+                    ForkJoinWorkerThread w = ws[i];
+                    if (w != null && w.sp != w.base)
+                        return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    // Support methods for ForkJoinTask
+
+    /**
+     * Returns an estimate of the number of tasks in the queue.
+     */
+    final int getQueueSize() {
+        // suppress momentarily negative values
+        return Math.max(0, sp - base);
+    }
+
+    /**
+     * Returns an estimate of the number of tasks, offset by a
+     * function of number of idle workers.
+     */
+    final int getEstimatedSurplusTaskCount() {
+        // The halving approximates weighting idle vs non-idle workers
+        return (sp - base) - (pool.getIdleThreadCount() >>> 1);
+    }
+
+    /**
+     * Scans, returning early if joinMe done.
+     */
+    final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
+        ForkJoinTask<?> t = pollTask();
+        if (t != null && joinMe.status < 0 && sp == base) {
+            pushTask(t); // unsteal if done and this task would be stealable
+            t = null;
+        }
+        return t;
+    }
+
+    /**
+     * Runs tasks until {@code pool.isQuiescent()}.
+     */
+    final void helpQuiescePool() {
+        for (;;) {
+            ForkJoinTask<?> t = pollTask();
+            if (t != null)
+                t.quietlyExec();
+            else if (tryInactivate() && pool.isQuiescent())
+                break;
+        }
+        do {} while (!tryActivate()); // re-activate on exit
+    }
+
+    // Unsafe mechanics
+
+    private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+    private static final long spOffset =
+        objectFieldOffset("sp", ForkJoinWorkerThread.class);
+    private static final long runStateOffset =
+        objectFieldOffset("runState", ForkJoinWorkerThread.class);
+    private static final long qBase;
+    private static final int qShift;
+
+    static {
+        qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
+        int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
+        if ((s & (s-1)) != 0)
+            throw new Error("data type scale not a power of two");
+        qShift = 31 - Integer.numberOfLeadingZeros(s);
+    }
+
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to corresponding Error
+            NoSuchFieldError error = new NoSuchFieldError(field);
+            error.initCause(e);
+            throw error;
+        }
+    }
+}

src/share/classes/java/util/concurrent/LinkedTransferQueue.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.util.AbstractQueue;
+import java.util.Collection;
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Queue;
+import java.util.concurrent.locks.LockSupport;
+/**
+ * An unbounded {@link TransferQueue} based on linked nodes.
+ * This queue orders elements FIFO (first-in-first-out) with respect
+ * to any given producer.  The <em>head</em> of the queue is that
+ * element that has been on the queue the longest time for some
+ * producer.  The <em>tail</em> of the queue is that element that has
+ * been on the queue the shortest time for some producer.
+ *
+ * <p>Beware that, unlike in most collections, the {@code size}
+ * method is <em>NOT</em> a constant-time operation. Because of the
+ * asynchronous nature of these queues, determining the current number
+ * of elements requires a traversal of the elements.
+ *
+ * <p>This class and its iterator implement all of the
+ * <em>optional</em> methods of the {@link Collection} and {@link
+ * Iterator} interfaces.
+ *
+ * <p>Memory consistency effects: As with other concurrent
+ * collections, actions in a thread prior to placing an object into a
+ * {@code LinkedTransferQueue}
+ * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * actions subsequent to the access or removal of that element from
+ * the {@code LinkedTransferQueue} in another thread.
+ *
+ * <p>This class is a member of the
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
+ * Java Collections Framework</a>.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ * @param <E> the type of elements held in this collection
+ */
+public class LinkedTransferQueue<E> extends AbstractQueue<E>
+    implements TransferQueue<E>, java.io.Serializable {
+    private static final long serialVersionUID = -3223113410248163686L;
+
+    /*
+     * *** Overview of Dual Queues with Slack ***
+     *
+     * Dual Queues, introduced by Scherer and Scott
+     * (http://www.cs.rice.edu/~wns1/papers/2004-DISC-DDS.pdf) are
+     * (linked) queues in which nodes may represent either data or
+     * requests.  When a thread tries to enqueue a data node, but
+     * encounters a request node, it instead "matches" and removes it;
+     * and vice versa for enqueuing requests. Blocking Dual Queues
+     * arrange that threads enqueuing unmatched requests block until
+     * other threads provide the match. Dual Synchronous Queues (see
+     * Scherer, Lea, & Scott
+     * http://www.cs.rochester.edu/u/scott/papers/2009_Scherer_CACM_SSQ.pdf)
+     * additionally arrange that threads enqueuing unmatched data also
+     * block.  Dual Transfer Queues support all of these modes, as
+     * dictated by callers.
+     *
+     * A FIFO dual queue may be implemented using a variation of the
+     * Michael & Scott (M&S) lock-free queue algorithm
+     * (http://www.cs.rochester.edu/u/scott/papers/1996_PODC_queues.pdf).
+     * It maintains two pointer fields, "head", pointing to a
+     * (matched) node that in turn points to the first actual
+     * (unmatched) queue node (or null if empty); and "tail" that
+     * points to the last node on the queue (or again null if
+     * empty). For example, here is a possible queue with four data
+     * elements:
+     *
+     *  head                tail
+     *    |                   |
+     *    v                   v
+     *    M -> U -> U -> U -> U
+     *
+     * The M&S queue algorithm is known to be prone to scalability and
+     * overhead limitations when maintaining (via CAS) these head and
+     * tail pointers. This has led to the development of
+     * contention-reducing variants such as elimination arrays (see
+     * Moir et al http://portal.acm.org/citation.cfm?id=1074013) and
+     * optimistic back pointers (see Ladan-Mozes & Shavit
+     * http://people.csail.mit.edu/edya/publications/OptimisticFIFOQueue-journal.pdf).
+     * However, the nature of dual queues enables a simpler tactic for
+     * improving M&S-style implementations when dual-ness is needed.
+     *
+     * In a dual queue, each node must atomically maintain its match
+     * status. While there are other possible variants, we implement
+     * this here as: for a data-mode node, matching entails CASing an
+     * "item" field from a non-null data value to null upon match, and
+     * vice-versa for request nodes, CASing from null to a data
+     * value. (Note that the linearization properties of this style of
+     * queue are easy to verify -- elements are made available by
+     * linking, and unavailable by matching.) Compared to plain M&S
+     * queues, this property of dual queues requires one additional
+     * successful atomic operation per enq/deq pair. But it also
+     * enables lower cost variants of queue maintenance mechanics. (A
+     * variation of this idea applies even for non-dual queues that
+     * support deletion of interior elements, such as
+     * j.u.c.ConcurrentLinkedQueue.)
+     *
+     * Once a node is matched, its match status can never again
+     * change.  We may thus arrange that the linked list of them
+     * contain a prefix of zero or more matched nodes, followed by a
+     * suffix of zero or more unmatched nodes. (Note that we allow
+     * both the prefix and suffix to be zero length, which in turn
+     * means that we do not use a dummy header.)  If we were not
+     * concerned with either time or space efficiency, we could
+     * correctly perform enqueue and dequeue operations by traversing
+     * from a pointer to the initial node; CASing the item of the
+     * first unmatched node on match and CASing the next field of the
+     * trailing node on appends. (Plus some special-casing when
+     * initially empty).  While this would be a terrible idea in
+     * itself, it does have the benefit of not requiring ANY atomic
+     * updates on head/tail fields.
+     *
+     * We introduce here an approach that lies between the extremes of
+     * never versus always updating queue (head and tail) pointers.
+     * This offers a tradeoff between sometimes requiring extra
+     * traversal steps to locate the first and/or last unmatched
+     * nodes, versus the reduced overhead and contention of fewer
+     * updates to queue pointers. For example, a possible snapshot of
+     * a queue is:
+     *
+     *  head           tail
+     *    |              |
+     *    v              v
+     *    M -> M -> U -> U -> U -> U
+     *
+     * The best value for this "slack" (the targeted maximum distance
+     * between the value of "head" and the first unmatched node, and
+     * similarly for "tail") is an empirical matter. We have found
+     * that using very small constants in the range of 1-3 work best
+     * over a range of platforms. Larger values introduce increasing
+     * costs of cache misses and risks of long traversal chains, while
+     * smaller values increase CAS contention and overhead.
+     *
+     * Dual queues with slack differ from plain M&S dual queues by
+     * virtue of only sometimes updating head or tail pointers when
+     * matching, appending, or even traversing nodes; in order to
+     * maintain a targeted slack.  The idea of "sometimes" may be
+     * operationalized in several ways. The simplest is to use a
+     * per-operation counter incremented on each traversal step, and
+     * to try (via CAS) to update the associated queue pointer
+     * whenever the count exceeds a threshold. Another, that requires
+     * more overhead, is to use random number generators to update
+     * with a given probability per traversal step.
+     *
+     * In any strategy along these lines, because CASes updating
+     * fields may fail, the actual slack may exceed targeted
+     * slack. However, they may be retried at any time to maintain
+     * targets.  Even when using very small slack values, this
+     * approach works well for dual queues because it allows all
+     * operations up to the point of matching or appending an item
+     * (hence potentially allowing progress by another thread) to be
+     * read-only, thus not introducing any further contention. As
+     * described below, we implement this by performing slack
+     * maintenance retries only after these points.
+     *
+     * As an accompaniment to such techniques, traversal overhead can
+     * be further reduced without increasing contention of head
+     * pointer updates: Threads may sometimes shortcut the "next" link
+     * path from the current "head" node to be closer to the currently
+     * known first unmatched node, and similarly for tail. Again, this
+     * may be triggered with using thresholds or randomization.
+     *
+     * These ideas must be further extended to avoid unbounded amounts
+     * of costly-to-reclaim garbage caused by the sequential "next"
+     * links of nodes starting at old forgotten head nodes: As first
+     * described in detail by Boehm
+     * (http://portal.acm.org/citation.cfm?doid=503272.503282) if a GC
+     * delays noticing that any arbitrarily old node has become
+     * garbage, all newer dead nodes will also be unreclaimed.
+     * (Similar issues arise in non-GC environments.)  To cope with
+     * this in our implementation, upon CASing to advance the head
+     * pointer, we set the "next" link of the previous head to point
+     * only to itself; thus limiting the length of connected dead lists.
+     * (We also take similar care to wipe out possibly garbage
+     * retaining values held in other Node fields.)  However, doing so
+     * adds some further complexity to traversal: If any "next"
+     * pointer links to itself, it indicates that the current thread
+     * has lagged behind a head-update, and so the traversal must
+     * continue from the "head".  Traversals trying to find the
+     * current tail starting from "tail" may also encounter
+     * self-links, in which case they also continue at "head".
+     *
+     * It is tempting in slack-based scheme to not even use CAS for
+     * updates (similarly to Ladan-Mozes & Shavit). However, this
+     * cannot be done for head updates under the above link-forgetting
+     * mechanics because an update may leave head at a detached node.
+     * And while direct writes are possible for tail updates, they
+     * increase the risk of long retraversals, and hence long garbage
+     * chains, which can be much more costly than is worthwhile
+     * considering that the cost difference of performing a CAS vs
+     * write is smaller when they are not triggered on each operation
+     * (especially considering that writes and CASes equally require
+     * additional GC bookkeeping ("write barriers") that are sometimes
+     * more costly than the writes themselves because of contention).
+     *
+     * Removal of interior nodes (due to timed out or interrupted
+     * waits, or calls to remove(x) or Iterator.remove) can use a
+     * scheme roughly similar to that described in Scherer, Lea, and
+     * Scott's SynchronousQueue. Given a predecessor, we can unsplice
+     * any node except the (actual) tail of the queue. To avoid
+     * build-up of cancelled trailing nodes, upon a request to remove
+     * a trailing node, it is placed in field "cleanMe" to be
+     * unspliced upon the next call to unsplice any other node.
+     * Situations needing such mechanics are not common but do occur
+     * in practice; for example when an unbounded series of short
+     * timed calls to poll repeatedly time out but never otherwise
+     * fall off the list because of an untimed call to take at the
+     * front of the queue. Note that maintaining field cleanMe does
+     * not otherwise much impact garbage retention even if never
+     * cleared by some other call because the held node will
+     * eventually either directly or indirectly lead to a self-link
+     * once off the list.
+     *
+     * *** Overview of implementation ***
+     *
+     * We use a threshold-based approach to updates, with a slack
+     * threshold of two -- that is, we update head/tail when the
+     * current pointer appears to be two or more steps away from the
+     * first/last node. The slack value is hard-wired: a path greater
+     * than one is naturally implemented by checking equality of
+     * traversal pointers except when the list has only one element,
+     * in which case we keep slack threshold at one. Avoiding tracking
+     * explicit counts across method calls slightly simplifies an
+     * already-messy implementation. Using randomization would
+     * probably work better if there were a low-quality dirt-cheap
+     * per-thread one available, but even ThreadLocalRandom is too
+     * heavy for these purposes.
+     *
+     * With such a small slack threshold value, it is rarely
+     * worthwhile to augment this with path short-circuiting; i.e.,
+     * unsplicing nodes between head and the first unmatched node, or
+     * similarly for tail, rather than advancing head or tail
+     * proper. However, it is used (in awaitMatch) immediately before
+     * a waiting thread starts to block, as a final bit of helping at
+     * a point when contention with others is extremely unlikely
+     * (since if other threads that could release it are operating,
+     * then the current thread wouldn't be blocking).
+     *
+     * We allow both the head and tail fields to be null before any
+     * nodes are enqueued; initializing upon first append.  This
+     * simplifies some other logic, as well as providing more
+     * efficient explicit control paths instead of letting JVMs insert
+     * implicit NullPointerExceptions when they are null.  While not
+     * currently fully implemented, we also leave open the possibility
+     * of re-nulling these fields when empty (which is complicated to
+     * arrange, for little benefit.)
+     *
+     * All enqueue/dequeue operations are handled by the single method
+     * "xfer" with parameters indicating whether to act as some form
+     * of offer, put, poll, take, or transfer (each possibly with
+     * timeout). The relative complexity of using one monolithic
+     * method outweighs the code bulk and maintenance problems of
+     * using separate methods for each case.
+     *
+     * Operation consists of up to three phases. The first is
+     * implemented within method xfer, the second in tryAppend, and
+     * the third in method awaitMatch.
+     *
+     * 1. Try to match an existing node
+     *
+     *    Starting at head, skip already-matched nodes until finding
+     *    an unmatched node of opposite mode, if one exists, in which
+     *    case matching it and returning, also if necessary updating
+     *    head to one past the matched node (or the node itself if the
+     *    list has no other unmatched nodes). If the CAS misses, then
+     *    a loop retries advancing head by two steps until either
+     *    success or the slack is at most two. By requiring that each
+     *    attempt advances head by two (if applicable), we ensure that
+     *    the slack does not grow without bound. Traversals also check
+     *    if the initial head is now off-list, in which case they
+     *    start at the new head.
+     *
+     *    If no candidates are found and the call was untimed
+     *    poll/offer, (argument "how" is NOW) return.
+     *
+     * 2. Try to append a new node (method tryAppend)
+     *
+     *    Starting at current tail pointer, find the actual last node
+     *    and try to append a new node (or if head was null, establish
+     *    the first node). Nodes can be appended only if their
+     *    predecessors are either already matched or are of the same
+     *    mode. If we detect otherwise, then a new node with opposite
+     *    mode must have been appended during traversal, so we must
+     *    restart at phase 1. The traversal and update steps are
+     *    otherwise similar to phase 1: Retrying upon CAS misses and
+     *    checking for staleness.  In particular, if a self-link is
+     *    encountered, then we can safely jump to a node on the list
+     *    by continuing the traversal at current head.
+     *
+     *    On successful append, if the call was ASYNC, return.
+     *
+     * 3. Await match or cancellation (method awaitMatch)
+     *
+     *    Wait for another thread to match node; instead cancelling if
+     *    the current thread was interrupted or the wait timed out. On
+     *    multiprocessors, we use front-of-queue spinning: If a node
+     *    appears to be the first unmatched node in the queue, it
+     *    spins a bit before blocking. In either case, before blocking
+     *    it tries to unsplice any nodes between the current "head"
+     *    and the first unmatched node.
+     *
+     *    Front-of-queue spinning vastly improves performance of
+     *    heavily contended queues. And so long as it is relatively
+     *    brief and "quiet", spinning does not much impact performance
+     *    of less-contended queues.  During spins threads check their
+     *    interrupt status and generate a thread-local random number
+     *    to decide to occasionally perform a Thread.yield. While
+     *    yield has underdefined specs, we assume that might it help,
+     *    and will not hurt in limiting impact of spinning on busy
+     *    systems.  We also use smaller (1/2) spins for nodes that are
+     *    not known to be front but whose predecessors have not
+     *    blocked -- these "chained" spins avoid artifacts of
+     *    front-of-queue rules which otherwise lead to alternating
+     *    nodes spinning vs blocking. Further, front threads that
+     *    represent phase changes (from data to request node or vice
+     *    versa) compared to their predecessors receive additional
+     *    chained spins, reflecting longer paths typically required to
+     *    unblock threads during phase changes.
+     */
+
+    /** True if on multiprocessor */
+    private static final boolean MP =
+        Runtime.getRuntime().availableProcessors() > 1;
+
+    /**
+     * The number of times to spin (with randomly interspersed calls
+     * to Thread.yield) on multiprocessor before blocking when a node
+     * is apparently the first waiter in the queue.  See above for
+     * explanation. Must be a power of two. The value is empirically
+     * derived -- it works pretty well across a variety of processors,
+     * numbers of CPUs, and OSes.
+     */
+    private static final int FRONT_SPINS   = 1 << 7;
+
+    /**
+     * The number of times to spin before blocking when a node is
+     * preceded by another node that is apparently spinning.  Also
+     * serves as an increment to FRONT_SPINS on phase changes, and as
+     * base average frequency for yielding during spins. Must be a
+     * power of two.
+     */
+    private static final int CHAINED_SPINS = FRONT_SPINS >>> 1;
+
+    /**
+     * Queue nodes. Uses Object, not E, for items to allow forgetting
+     * them after use.  Relies heavily on Unsafe mechanics to minimize
+     * unnecessary ordering constraints: Writes that intrinsically
+     * precede or follow CASes use simple relaxed forms.  Other
+     * cleanups use releasing/lazy writes.
+     */
+    static final class Node {
+        final boolean isData;   // false if this is a request node
+        volatile Object item;   // initially non-null if isData; CASed to match
+        volatile Node next;
+        volatile Thread waiter; // null until waiting
+
+        // CAS methods for fields
+        final boolean casNext(Node cmp, Node val) {
+            return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
+        }
+
+        final boolean casItem(Object cmp, Object val) {
+            // assert cmp == null || cmp.getClass() != Node.class;
+            return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val);
+        }
+
+        /**
+         * Creates a new node. Uses relaxed write because item can only
+         * be seen if followed by CAS.
+         */
+        Node(Object item, boolean isData) {
+            UNSAFE.putObject(this, itemOffset, item); // relaxed write
+            this.isData = isData;
+        }
+
+        /**
+         * Links node to itself to avoid garbage retention.  Called
+         * only after CASing head field, so uses relaxed write.
+         */
+        final void forgetNext() {
+            UNSAFE.putObject(this, nextOffset, this);
+        }
+
+        /**
+         * Sets item to self (using a releasing/lazy write) and waiter
+         * to null, to avoid garbage retention after extracting or
+         * cancelling.
+         */
+        final void forgetContents() {
+            UNSAFE.putOrderedObject(this, itemOffset, this);
+            UNSAFE.putOrderedObject(this, waiterOffset, null);
+        }
+
+        /**
+         * Returns true if this node has been matched, including the
+         * case of artificial matches due to cancellation.
+         */
+        final boolean isMatched() {
+            Object x = item;
+            return (x == this) || ((x == null) == isData);
+        }
+
+        /**
+         * Returns true if this is an unmatched request node.
+         */
+        final boolean isUnmatchedRequest() {
+            return !isData && item == null;
+        }
+
+        /**
+         * Returns true if a node with the given mode cannot be
+         * appended to this node because this node is unmatched and
+         * has opposite data mode.
+         */
+        final boolean cannotPrecede(boolean haveData) {
+            boolean d = isData;
+            Object x;
+            return d != haveData && (x = item) != this && (x != null) == d;
+        }
+
+        /**
+         * Tries to artificially match a data node -- used by remove.
+         */
+        final boolean tryMatchData() {
+            // assert isData;
+            Object x = item;
+            if (x != null && x != this && casItem(x, null)) {
+                LockSupport.unpark(waiter);
+                return true;
+            }
+            return false;
+        }
+
+        // Unsafe mechanics
+        private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+        private static final long nextOffset =
+            objectFieldOffset(UNSAFE, "next", Node.class);
+        private static final long itemOffset =
+            objectFieldOffset(UNSAFE, "item", Node.class);
+        private static final long waiterOffset =
+            objectFieldOffset(UNSAFE, "waiter", Node.class);
+
+        private static final long serialVersionUID = -3375979862319811754L;
+    }
+
+    /** head of the queue; null until first enqueue */
+    transient volatile Node head;
+
+    /** predecessor of dangling unspliceable node */
+    private transient volatile Node cleanMe; // decl here reduces contention
+
+    /** tail of the queue; null until first append */
+    private transient volatile Node tail;
+
+    // CAS methods for fields
+    private boolean casTail(Node cmp, Node val) {
+        return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val);
+    }
+
+    private boolean casHead(Node cmp, Node val) {
+        return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
+    }
+
+    private boolean casCleanMe(Node cmp, Node val) {
+        return UNSAFE.compareAndSwapObject(this, cleanMeOffset, cmp, val);
+    }
+
+    /*
+     * Possible values for "how" argument in xfer method.
+     */
+    private static final int NOW   = 0; // for untimed poll, tryTransfer
+    private static final int ASYNC = 1; // for offer, put, add
+    private static final int SYNC  = 2; // for transfer, take
+    private static final int TIMED = 3; // for timed poll, tryTransfer
+
+    @SuppressWarnings("unchecked")
+    static <E> E cast(Object item) {
+        // assert item == null || item.getClass() != Node.class;
+        return (E) item;
+    }
+
+    /**
+     * Implements all queuing methods. See above for explanation.
+     *
+     * @param e the item or null for take
+     * @param haveData true if this is a put, else a take
+     * @param how NOW, ASYNC, SYNC, or TIMED
+     * @param nanos timeout in nanosecs, used only if mode is TIMED
+     * @return an item if matched, else e
+     * @throws NullPointerException if haveData mode but e is null
+     */
+    private E xfer(E e, boolean haveData, int how, long nanos) {
+        if (haveData && (e == null))
+            throw new NullPointerException();
+        Node s = null;                        // the node to append, if needed
+
+        retry: for (;;) {                     // restart on append race
+
+            for (Node h = head, p = h; p != null;) { // find & match first node
+                boolean isData = p.isData;
+                Object item = p.item;
+                if (item != p && (item != null) == isData) { // unmatched
+                    if (isData == haveData)   // can't match
+                        break;
+                    if (p.casItem(item, e)) { // match
+                        for (Node q = p; q != h;) {
+                            Node n = q.next;  // update head by 2
+                            if (n != null)    // unless singleton
+                                q = n;
+                            if (head == h && casHead(h, q)) {
+                                h.forgetNext();
+                                break;
+                            }                 // advance and retry
+                            if ((h = head)   == null ||
+                                (q = h.next) == null || !q.isMatched())
+                                break;        // unless slack < 2
+                        }
+                        LockSupport.unpark(p.waiter);
+                        return this.<E>cast(item);
+                    }
+                }
+                Node n = p.next;
+                p = (p != n) ? n : (h = head); // Use head if p offlist
+            }
+
+            if (how != NOW) {                 // No matches available
+                if (s == null)
+                    s = new Node(e, haveData);
+                Node pred = tryAppend(s, haveData);
+                if (pred == null)
+                    continue retry;           // lost race vs opposite mode
+                if (how != ASYNC)
+                    return awaitMatch(s, pred, e, (how == TIMED), nanos);
+            }
+            return e; // not waiting
+        }
+    }
+
+    /**
+     * Tries to append node s as tail.
+     *
+     * @param s the node to append
+     * @param haveData true if appending in data mode
+     * @return null on failure due to losing race with append in
+     * different mode, else s's predecessor, or s itself if no
+     * predecessor
+     */
+    private Node tryAppend(Node s, boolean haveData) {
+        for (Node t = tail, p = t;;) {        // move p to last node and append
+            Node n, u;                        // temps for reads of next & tail
+            if (p == null && (p = head) == null) {
+                if (casHead(null, s))
+                    return s;                 // initialize
+            }
+            else if (p.cannotPrecede(haveData))
+                return null;                  // lost race vs opposite mode
+            else if ((n = p.next) != null)    // not last; keep traversing
+                p = p != t && t != (u = tail) ? (t = u) : // stale tail
+                    (p != n) ? n : null;      // restart if off list
+            else if (!p.casNext(null, s))
+                p = p.next;                   // re-read on CAS failure
+            else {
+                if (p != t) {                 // update if slack now >= 2
+                    while ((tail != t || !casTail(t, s)) &&
+                           (t = tail)   != null &&
+                           (s = t.next) != null && // advance and retry
+                           (s = s.next) != null && s != t);
+                }
+                return p;
+            }
+        }
+    }
+
+    /**
+     * Spins/yields/blocks until node s is matched or caller gives up.
+     *
+     * @param s the waiting node
+     * @param pred the predecessor of s, or s itself if it has no
+     * predecessor, or null if unknown (the null case does not occur
+     * in any current calls but may in possible future extensions)
+     * @param e the comparison value for checking match
+     * @param timed if true, wait only until timeout elapses
+     * @param nanos timeout in nanosecs, used only if timed is true
+     * @return matched item, or e if unmatched on interrupt or timeout
+     */
+    private E awaitMatch(Node s, Node pred, E e, boolean timed, long nanos) {
+        long lastTime = timed ? System.nanoTime() : 0L;
+        Thread w = Thread.currentThread();
+        int spins = -1; // initialized after first item and cancel checks
+        ThreadLocalRandom randomYields = null; // bound if needed
+
+        for (;;) {
+            Object item = s.item;
+            if (item != e) {                  // matched
+                // assert item != s;
+                s.forgetContents();           // avoid garbage
+                return this.<E>cast(item);
+            }
+            if ((w.isInterrupted() || (timed && nanos <= 0)) &&
+                    s.casItem(e, s)) {       // cancel
+                unsplice(pred, s);
+                return e;
+            }
+
+            if (spins < 0) {                  // establish spins at/near front
+                if ((spins = spinsFor(pred, s.isData)) > 0)
+                    randomYields = ThreadLocalRandom.current();
+            }
+            else if (spins > 0) {             // spin
+                if (--spins == 0)
+                    shortenHeadPath();        // reduce slack before blocking
+                else if (randomYields.nextInt(CHAINED_SPINS) == 0)
+                    Thread.yield();           // occasionally yield
+            }
+            else if (s.waiter == null) {
+                s.waiter = w;                 // request unpark then recheck
+            }
+            else if (timed) {
+                long now = System.nanoTime();
+                if ((nanos -= now - lastTime) > 0)
+                    LockSupport.parkNanos(this, nanos);
+                lastTime = now;
+            }
+            else {
+                LockSupport.park(this);
+                s.waiter = null;
+                spins = -1;                   // spin if front upon wakeup
+            }
+        }
+    }
+
+    /**
+     * Returns spin/yield value for a node with given predecessor and
+     * data mode. See above for explanation.
+     */
+    private static int spinsFor(Node pred, boolean haveData) {
+        if (MP && pred != null) {
+            if (pred.isData != haveData)      // phase change
+                return FRONT_SPINS + CHAINED_SPINS;
+            if (pred.isMatched())             // probably at front
+                return FRONT_SPINS;
+            if (pred.waiter == null)          // pred apparently spinning
+                return CHAINED_SPINS;
+        }
+        return 0;
+    }
+
+    /**
+     * Tries (once) to unsplice nodes between head and first unmatched
+     * or trailing node; failing on contention.
+     */
+    private void shortenHeadPath() {
+        Node h, hn, p, q;
+        if ((p = h = head) != null && h.isMatched() &&
+            (q = hn = h.next) != null) {
+            Node n;
+            while ((n = q.next) != q) {
+                if (n == null || !q.isMatched()) {
+                    if (hn != q && h.next == hn)
+                        h.casNext(hn, q);
+                    break;
+                }
+                p = q;
+                q = n;
+            }
+        }
+    }
+
+    /* -------------- Traversal methods -------------- */
+
+    /**
+     * Returns the successor of p, or the head node if p.next has been
+     * linked to self, which will only be true if traversing with a
+     * stale pointer that is now off the list.
+     */
+    final Node succ(Node p) {
+        Node next = p.next;
+        return (p == next) ? head : next;
+    }
+
+    /**
+     * Returns the first unmatched node of the given mode, or null if
+     * none.  Used by methods isEmpty, hasWaitingConsumer.
+     */
+    private Node firstOfMode(boolean isData) {
+        for (Node p = head; p != null; p = succ(p)) {
+            if (!p.isMatched())
+                return (p.isData == isData) ? p : null;
+        }
+        return null;
+    }
+
+    /**
+     * Returns the item in the first unmatched node with isData; or
+     * null if none.  Used by peek.
+     */
+    private E firstDataItem() {
+        for (Node p = head; p != null; p = succ(p)) {
+            Object item = p.item;
+            if (p.isData) {
+                if (item != null && item != p)
+                    return this.<E>cast(item);
+            }
+            else if (item == null)
+                return null;
+        }
+        return null;
+    }
+
+    /**
+     * Traverses and counts unmatched nodes of the given mode.
+     * Used by methods size and getWaitingConsumerCount.
+     */
+    private int countOfMode(boolean data) {
+        int count = 0;
+        for (Node p = head; p != null; ) {
+            if (!p.isMatched()) {
+                if (p.isData != data)
+                    return 0;
+                if (++count == Integer.MAX_VALUE) // saturated
+                    break;
+            }
+            Node n = p.next;
+            if (n != p)
+                p = n;
+            else {
+                count = 0;
+                p = head;
+            }
+        }
+        return count;
+    }
+
+    final class Itr implements Iterator<E> {
+        private Node nextNode;   // next node to return item for
+        private E nextItem;      // the corresponding item
+        private Node lastRet;    // last returned node, to support remove
+        private Node lastPred;   // predecessor to unlink lastRet
+
+        /**
+         * Moves to next node after prev, or first node if prev null.
+         */
+        private void advance(Node prev) {
+            lastPred = lastRet;
+            lastRet = prev;
+            for (Node p = (prev == null) ? head : succ(prev);
+                 p != null; p = succ(p)) {
+                Object item = p.item;
+                if (p.isData) {
+                    if (item != null && item != p) {
+                        nextItem = LinkedTransferQueue.this.<E>cast(item);
+                        nextNode = p;
+                        return;
+                    }
+                }
+                else if (item == null)
+                    break;
+            }
+            nextNode = null;
+        }
+
+        Itr() {
+            advance(null);
+        }
+
+        public final boolean hasNext() {
+            return nextNode != null;
+        }
+
+        public final E next() {
+            Node p = nextNode;
+            if (p == null) throw new NoSuchElementException();
+            E e = nextItem;
+            advance(p);
+            return e;
+        }
+
+        public final void remove() {
+            Node p = lastRet;
+            if (p == null) throw new IllegalStateException();
+            findAndRemoveDataNode(lastPred, p);
+        }
+    }
+
+    /* -------------- Removal methods -------------- */
+
+    /**
+     * Unsplices (now or later) the given deleted/cancelled node with
+     * the given predecessor.
+     *
+     * @param pred predecessor of node to be unspliced
+     * @param s the node to be unspliced
+     */
+    private void unsplice(Node pred, Node s) {
+        s.forgetContents(); // clear unneeded fields
+        /*
+         * At any given time, exactly one node on list cannot be
+         * unlinked -- the last inserted node. To accommodate this, if
+         * we cannot unlink s, we save its predecessor as "cleanMe",
+         * processing the previously saved version first. Because only
+         * one node in the list can have a null next, at least one of
+         * node s or the node previously saved can always be
+         * processed, so this always terminates.
+         */
+        if (pred != null && pred != s) {
+            while (pred.next == s) {
+                Node oldpred = (cleanMe == null) ? null : reclean();
+                Node n = s.next;
+                if (n != null) {
+                    if (n != s)
+                        pred.casNext(s, n);
+                    break;
+                }
+                if (oldpred == pred ||      // Already saved
+                    ((oldpred == null || oldpred.next == s) &&
+                     casCleanMe(oldpred, pred))) {
+                    break;
+                }
+            }
+        }
+    }
+
+    /**
+     * Tries to unsplice the deleted/cancelled node held in cleanMe
+     * that was previously uncleanable because it was at tail.
+     *
+     * @return current cleanMe node (or null)
+     */
+    private Node reclean() {
+        /*
+         * cleanMe is, or at one time was, predecessor of a cancelled
+         * node s that was the tail so could not be unspliced.  If it
+         * is no longer the tail, try to unsplice if necessary and
+         * make cleanMe slot available.  This differs from similar
+         * code in unsplice() because we must check that pred still
+         * points to a matched node that can be unspliced -- if not,
+         * we can (must) clear cleanMe without unsplicing.  This can
+         * loop only due to contention.
+         */
+        Node pred;
+        while ((pred = cleanMe) != null) {
+            Node s = pred.next;
+            Node n;
+            if (s == null || s == pred || !s.isMatched())
+                casCleanMe(pred, null); // already gone
+            else if ((n = s.next) != null) {
+                if (n != s)
+                    pred.casNext(s, n);
+                casCleanMe(pred, null);
+            }
+            else
+                break;
+        }
+        return pred;
+    }
+
+    /**
+     * Main implementation of Iterator.remove(). Finds
+     * and unsplices the given data node.
+     *
+     * @param possiblePred possible predecessor of s
+     * @param s the node to remove
+     */
+    final void findAndRemoveDataNode(Node possiblePred, Node s) {
+        // assert s.isData;
+        if (s.tryMatchData()) {
+            if (possiblePred != null && possiblePred.next == s)
+                unsplice(possiblePred, s); // was actual predecessor
+            else {
+                for (Node pred = null, p = head; p != null; ) {
+                    if (p == s) {
+                        unsplice(pred, p);
+                        break;
+                    }
+                    if (p.isUnmatchedRequest())
+                        break;
+                    pred = p;
+                    if ((p = p.next) == pred) { // stale
+                        pred = null;
+                        p = head;
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Main implementation of remove(Object)
+     */
+    private boolean findAndRemove(Object e) {
+        if (e != null) {
+            for (Node pred = null, p = head; p != null; ) {
+                Object item = p.item;
+                if (p.isData) {
+                    if (item != null && item != p && e.equals(item) &&
+                        p.tryMatchData()) {
+                        unsplice(pred, p);
+                        return true;
+                    }
+                }
+                else if (item == null)
+                    break;
+                pred = p;
+                if ((p = p.next) == pred) { // stale
+                    pred = null;
+                    p = head;
+                }
+            }
+        }
+        return false;
+    }
+
+
+    /**
+     * Creates an initially empty {@code LinkedTransferQueue}.
+     */
+    public LinkedTransferQueue() {
+    }
+
+    /**
+     * Creates a {@code LinkedTransferQueue}
+     * initially containing the elements of the given collection,
+     * added in traversal order of the collection's iterator.
+     *
+     * @param c the collection of elements to initially contain
+     * @throws NullPointerException if the specified collection or any
+     *         of its elements are null
+     */
+    public LinkedTransferQueue(Collection<? extends E> c) {
+        this();
+        addAll(c);
+    }
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     * As the queue is unbounded, this method will never block.
+     *
+     * @throws NullPointerException if the specified element is null
+     */
+    public void put(E e) {
+        xfer(e, true, ASYNC, 0);
+    }
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     * As the queue is unbounded, this method will never block or
+     * return {@code false}.
+     *
+     * @return {@code true} (as specified by
+     *  {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer})
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean offer(E e, long timeout, TimeUnit unit) {
+        xfer(e, true, ASYNC, 0);
+        return true;
+    }
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     * As the queue is unbounded, this method will never return {@code false}.
+     *
+     * @return {@code true} (as specified by
+     *         {@link BlockingQueue#offer(Object) BlockingQueue.offer})
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean offer(E e) {
+        xfer(e, true, ASYNC, 0);
+        return true;
+    }
+
+    /**
+     * Inserts the specified element at the tail of this queue.
+     * As the queue is unbounded, this method will never throw
+     * {@link IllegalStateException} or return {@code false}.
+     *
+     * @return {@code true} (as specified by {@link Collection#add})
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean add(E e) {
+        xfer(e, true, ASYNC, 0);
+        return true;
+    }
+
+    /**
+     * Transfers the element to a waiting consumer immediately, if possible.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * otherwise returning {@code false} without enqueuing the element.
+     *
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean tryTransfer(E e) {
+        return xfer(e, true, NOW, 0) == null;
+    }
+
+    /**
+     * Transfers the element to a consumer, waiting if necessary to do so.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * else inserts the specified element at the tail of this queue
+     * and waits until the element is received by a consumer.
+     *
+     * @throws NullPointerException if the specified element is null
+     */
+    public void transfer(E e) throws InterruptedException {
+        if (xfer(e, true, SYNC, 0) != null) {
+            Thread.interrupted(); // failure possible only due to interrupt
+            throw new InterruptedException();
+        }
+    }
+
+    /**
+     * Transfers the element to a consumer if it is possible to do so
+     * before the timeout elapses.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * else inserts the specified element at the tail of this queue
+     * and waits until the element is received by a consumer,
+     * returning {@code false} if the specified wait time elapses
+     * before the element can be transferred.
+     *
+     * @throws NullPointerException if the specified element is null
+     */
+    public boolean tryTransfer(E e, long timeout, TimeUnit unit)
+        throws InterruptedException {
+        if (xfer(e, true, TIMED, unit.toNanos(timeout)) == null)
+            return true;
+        if (!Thread.interrupted())
+            return false;
+        throw new InterruptedException();
+    }
+
+    public E take() throws InterruptedException {
+        E e = xfer(null, false, SYNC, 0);
+        if (e != null)
+            return e;
+        Thread.interrupted();
+        throw new InterruptedException();
+    }
+
+    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
+        E e = xfer(null, false, TIMED, unit.toNanos(timeout));
+        if (e != null || !Thread.interrupted())
+            return e;
+        throw new InterruptedException();
+    }
+
+    public E poll() {
+        return xfer(null, false, NOW, 0);
+    }
+
+    /**
+     * @throws NullPointerException     {@inheritDoc}
+     * @throws IllegalArgumentException {@inheritDoc}
+     */
+    public int drainTo(Collection<? super E> c) {
+        if (c == null)
+            throw new NullPointerException();
+        if (c == this)
+            throw new IllegalArgumentException();
+        int n = 0;
+        E e;
+        while ( (e = poll()) != null) {
+            c.add(e);
+            ++n;
+        }
+        return n;
+    }
+
+    /**
+     * @throws NullPointerException     {@inheritDoc}
+     * @throws IllegalArgumentException {@inheritDoc}
+     */
+    public int drainTo(Collection<? super E> c, int maxElements) {
+        if (c == null)
+            throw new NullPointerException();
+        if (c == this)
+            throw new IllegalArgumentException();
+        int n = 0;
+        E e;
+        while (n < maxElements && (e = poll()) != null) {
+            c.add(e);
+            ++n;
+        }
+        return n;
+    }
+
+    /**
+     * Returns an iterator over the elements in this queue in proper
+     * sequence, from head to tail.
+     *
+     * <p>The returned iterator is a "weakly consistent" iterator that
+     * will never throw
+     * {@link ConcurrentModificationException ConcurrentModificationException},
+     * and guarantees to traverse elements as they existed upon
+     * construction of the iterator, and may (but is not guaranteed
+     * to) reflect any modifications subsequent to construction.
+     *
+     * @return an iterator over the elements in this queue in proper sequence
+     */
+    public Iterator<E> iterator() {
+        return new Itr();
+    }
+
+    public E peek() {
+        return firstDataItem();
+    }
+
+    /**
+     * Returns {@code true} if this queue contains no elements.
+     *
+     * @return {@code true} if this queue contains no elements
+     */
+    public boolean isEmpty() {
+        return firstOfMode(true) == null;
+    }
+
+    public boolean hasWaitingConsumer() {
+        return firstOfMode(false) != null;
+    }
+
+    /**
+     * Returns the number of elements in this queue.  If this queue
+     * contains more than {@code Integer.MAX_VALUE} elements, returns
+     * {@code Integer.MAX_VALUE}.
+     *
+     * <p>Beware that, unlike in most collections, this method is
+     * <em>NOT</em> a constant-time operation. Because of the
+     * asynchronous nature of these queues, determining the current
+     * number of elements requires an O(n) traversal.
+     *
+     * @return the number of elements in this queue
+     */
+    public int size() {
+        return countOfMode(true);
+    }
+
+    public int getWaitingConsumerCount() {
+        return countOfMode(false);
+    }
+
+    /**
+     * Removes a single instance of the specified element from this queue,
+     * if it is present.  More formally, removes an element {@code e} such
+     * that {@code o.equals(e)}, if this queue contains one or more such
+     * elements.
+     * Returns {@code true} if this queue contained the specified element
+     * (or equivalently, if this queue changed as a result of the call).
+     *
+     * @param o element to be removed from this queue, if present
+     * @return {@code true} if this queue changed as a result of the call
+     */
+    public boolean remove(Object o) {
+        return findAndRemove(o);
+    }
+
+    /**
+     * Always returns {@code Integer.MAX_VALUE} because a
+     * {@code LinkedTransferQueue} is not capacity constrained.
+     *
+     * @return {@code Integer.MAX_VALUE} (as specified by
+     *         {@link BlockingQueue#remainingCapacity()})
+     */
+    public int remainingCapacity() {
+        return Integer.MAX_VALUE;
+    }
+
+    /**
+     * Saves the state to a stream (that is, serializes it).
+     *
+     * @serialData All of the elements (each an {@code E}) in
+     * the proper order, followed by a null
+     * @param s the stream
+     */
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+        s.defaultWriteObject();
+        for (E e : this)
+            s.writeObject(e);
+        // Use trailing null as sentinel
+        s.writeObject(null);
+    }
+
+    /**
+     * Reconstitutes the Queue instance from a stream (that is,
+     * deserializes it).
+     *
+     * @param s the stream
+     */
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        s.defaultReadObject();
+        for (;;) {
+            @SuppressWarnings("unchecked") E item = (E) s.readObject();
+            if (item == null)
+                break;
+            else
+                offer(item);
+        }
+    }
+
+    // Unsafe mechanics
+
+    private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+    private static final long headOffset =
+        objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class);
+    private static final long tailOffset =
+        objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class);
+    private static final long cleanMeOffset =
+        objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class);
+
+    static long objectFieldOffset(sun.misc.Unsafe UNSAFE,
+                                  String field, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to corresponding Error
+            NoSuchFieldError error = new NoSuchFieldError(field);
+            error.initCause(e);
+            throw error;
+        }
+    }
+
+}

src/share/classes/java/util/concurrent/Phaser.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.LockSupport;
+
+/**
+ * A reusable synchronization barrier, similar in functionality to
+ * {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and
+ * {@link java.util.concurrent.CountDownLatch CountDownLatch}
+ * but supporting more flexible usage.
+ *
+ * <p> <b>Registration.</b> Unlike the case for other barriers, the
+ * number of parties <em>registered</em> to synchronize on a phaser
+ * may vary over time.  Tasks may be registered at any time (using
+ * methods {@link #register}, {@link #bulkRegister}, or forms of
+ * constructors establishing initial numbers of parties), and
+ * optionally deregistered upon any arrival (using {@link
+ * #arriveAndDeregister}).  As is the case with most basic
+ * synchronization constructs, registration and deregistration affect
+ * only internal counts; they do not establish any further internal
+ * bookkeeping, so tasks cannot query whether they are registered.
+ * (However, you can introduce such bookkeeping by subclassing this
+ * class.)
+ *
+ * <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
+ * Phaser} may be repeatedly awaited.  Method {@link
+ * #arriveAndAwaitAdvance} has effect analogous to {@link
+ * java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each
+ * generation of a {@code Phaser} has an associated phase number. The
+ * phase number starts at zero, and advances when all parties arrive
+ * at the barrier, wrapping around to zero after reaching {@code
+ * Integer.MAX_VALUE}. The use of phase numbers enables independent
+ * control of actions upon arrival at a barrier and upon awaiting
+ * others, via two kinds of methods that may be invoked by any
+ * registered party:
+ *
+ * <ul>
+ *
+ *   <li> <b>Arrival.</b> Methods {@link #arrive} and
+ *       {@link #arriveAndDeregister} record arrival at a
+ *       barrier. These methods do not block, but return an associated
+ *       <em>arrival phase number</em>; that is, the phase number of
+ *       the barrier to which the arrival applied. When the final
+ *       party for a given phase arrives, an optional barrier action
+ *       is performed and the phase advances.  Barrier actions,
+ *       performed by the party triggering a phase advance, are
+ *       arranged by overriding method {@link #onAdvance(int, int)},
+ *       which also controls termination. Overriding this method is
+ *       similar to, but more flexible than, providing a barrier
+ *       action to a {@code CyclicBarrier}.
+ *
+ *   <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an
+ *       argument indicating an arrival phase number, and returns when
+ *       the barrier advances to (or is already at) a different phase.
+ *       Unlike similar constructions using {@code CyclicBarrier},
+ *       method {@code awaitAdvance} continues to wait even if the
+ *       waiting thread is interrupted. Interruptible and timeout
+ *       versions are also available, but exceptions encountered while
+ *       tasks wait interruptibly or with timeout do not change the
+ *       state of the barrier. If necessary, you can perform any
+ *       associated recovery within handlers of those exceptions,
+ *       often after invoking {@code forceTermination}.  Phasers may
+ *       also be used by tasks executing in a {@link ForkJoinPool},
+ *       which will ensure sufficient parallelism to execute tasks
+ *       when others are blocked waiting for a phase to advance.
+ *
+ * </ul>
+ *
+ * <p> <b>Termination.</b> A {@code Phaser} may enter a
+ * <em>termination</em> state in which all synchronization methods
+ * immediately return without updating phaser state or waiting for
+ * advance, and indicating (via a negative phase value) that execution
+ * is complete.  Termination is triggered when an invocation of {@code
+ * onAdvance} returns {@code true}.  As illustrated below, when
+ * phasers control actions with a fixed number of iterations, it is
+ * often convenient to override this method to cause termination when
+ * the current phase number reaches a threshold. Method {@link
+ * #forceTermination} is also available to abruptly release waiting
+ * threads and allow them to terminate.
+ *
+ * <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged
+ * in tree structures) to reduce contention. Phasers with large
+ * numbers of parties that would otherwise experience heavy
+ * synchronization contention costs may instead be set up so that
+ * groups of sub-phasers share a common parent.  This may greatly
+ * increase throughput even though it incurs greater per-operation
+ * overhead.
+ *
+ * <p><b>Monitoring.</b> While synchronization methods may be invoked
+ * only by registered parties, the current state of a phaser may be
+ * monitored by any caller.  At any given moment there are {@link
+ * #getRegisteredParties} parties in total, of which {@link
+ * #getArrivedParties} have arrived at the current phase ({@link
+ * #getPhase}).  When the remaining ({@link #getUnarrivedParties})
+ * parties arrive, the phase advances.  The values returned by these
+ * methods may reflect transient states and so are not in general
+ * useful for synchronization control.  Method {@link #toString}
+ * returns snapshots of these state queries in a form convenient for
+ * informal monitoring.
+ *
+ * <p><b>Sample usages:</b>
+ *
+ * <p>A {@code Phaser} may be used instead of a {@code CountDownLatch}
+ * to control a one-shot action serving a variable number of
+ * parties. The typical idiom is for the method setting this up to
+ * first register, then start the actions, then deregister, as in:
+ *
+ *  <pre> {@code
+ * void runTasks(List<Runnable> tasks) {
+ *   final Phaser phaser = new Phaser(1); // "1" to register self
+ *   // create and start threads
+ *   for (Runnable task : tasks) {
+ *     phaser.register();
+ *     new Thread() {
+ *       public void run() {
+ *         phaser.arriveAndAwaitAdvance(); // await all creation
+ *         task.run();
+ *       }
+ *     }.start();
+ *   }
+ *
+ *   // allow threads to start and deregister self
+ *   phaser.arriveAndDeregister();
+ * }}</pre>
+ *
+ * <p>One way to cause a set of threads to repeatedly perform actions
+ * for a given number of iterations is to override {@code onAdvance}:
+ *
+ *  <pre> {@code
+ * void startTasks(List<Runnable> tasks, final int iterations) {
+ *   final Phaser phaser = new Phaser() {
+ *     protected boolean onAdvance(int phase, int registeredParties) {
+ *       return phase >= iterations || registeredParties == 0;
+ *     }
+ *   };
+ *   phaser.register();
+ *   for (final Runnable task : tasks) {
+ *     phaser.register();
+ *     new Thread() {
+ *       public void run() {
+ *         do {
+ *           task.run();
+ *           phaser.arriveAndAwaitAdvance();
+ *         } while (!phaser.isTerminated());
+ *       }
+ *     }.start();
+ *   }
+ *   phaser.arriveAndDeregister(); // deregister self, don't wait
+ * }}</pre>
+ *
+ * If the main task must later await termination, it
+ * may re-register and then execute a similar loop:
+ *  <pre> {@code
+ *   // ...
+ *   phaser.register();
+ *   while (!phaser.isTerminated())
+ *     phaser.arriveAndAwaitAdvance();}</pre>
+ *
+ * <p>Related constructions may be used to await particular phase numbers
+ * in contexts where you are sure that the phase will never wrap around
+ * {@code Integer.MAX_VALUE}. For example:
+ *
+ *  <pre> {@code
+ * void awaitPhase(Phaser phaser, int phase) {
+ *   int p = phaser.register(); // assumes caller not already registered
+ *   while (p < phase) {
+ *     if (phaser.isTerminated())
+ *       // ... deal with unexpected termination
+ *     else
+ *       p = phaser.arriveAndAwaitAdvance();
+ *   }
+ *   phaser.arriveAndDeregister();
+ * }}</pre>
+ *
+ *
+ * <p>To create a set of tasks using a tree of phasers,
+ * you could use code of the following form, assuming a
+ * Task class with a constructor accepting a phaser that
+ * it registers for upon construction:
+ *
+ *  <pre> {@code
+ * void build(Task[] actions, int lo, int hi, Phaser ph) {
+ *   if (hi - lo > TASKS_PER_PHASER) {
+ *     for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
+ *       int j = Math.min(i + TASKS_PER_PHASER, hi);
+ *       build(actions, i, j, new Phaser(ph));
+ *     }
+ *   } else {
+ *     for (int i = lo; i < hi; ++i)
+ *       actions[i] = new Task(ph);
+ *       // assumes new Task(ph) performs ph.register()
+ *   }
+ * }
+ * // .. initially called, for n tasks via
+ * build(new Task[n], 0, n, new Phaser());}</pre>
+ *
+ * The best value of {@code TASKS_PER_PHASER} depends mainly on
+ * expected barrier synchronization rates. A value as low as four may
+ * be appropriate for extremely small per-barrier task bodies (thus
+ * high rates), or up to hundreds for extremely large ones.
+ *
+ * </pre>
+ *
+ * <p><b>Implementation notes</b>: This implementation restricts the
+ * maximum number of parties to 65535. Attempts to register additional
+ * parties result in {@code IllegalStateException}. However, you can and
+ * should create tiered phasers to accommodate arbitrarily large sets
+ * of participants.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class Phaser {
+    /*
+     * This class implements an extension of X10 "clocks".  Thanks to
+     * Vijay Saraswat for the idea, and to Vivek Sarkar for
+     * enhancements to extend functionality.
+     */
+
+    /**
+     * Barrier state representation. Conceptually, a barrier contains
+     * four values:
+     *
+     * * parties -- the number of parties to wait (16 bits)
+     * * unarrived -- the number of parties yet to hit barrier (16 bits)
+     * * phase -- the generation of the barrier (31 bits)
+     * * terminated -- set if barrier is terminated (1 bit)
+     *
+     * However, to efficiently maintain atomicity, these values are
+     * packed into a single (atomic) long. Termination uses the sign
+     * bit of 32 bit representation of phase, so phase is set to -1 on
+     * termination. Good performance relies on keeping state decoding
+     * and encoding simple, and keeping race windows short.
+     *
+     * Note: there are some cheats in arrive() that rely on unarrived
+     * count being lowest 16 bits.
+     */
+    private volatile long state;
+
+    private static final int ushortMask = 0xffff;
+    private static final int phaseMask  = 0x7fffffff;
+
+    private static int unarrivedOf(long s) {
+        return (int) (s & ushortMask);
+    }
+
+    private static int partiesOf(long s) {
+        return ((int) s) >>> 16;
+    }
+
+    private static int phaseOf(long s) {
+        return (int) (s >>> 32);
+    }
+
+    private static int arrivedOf(long s) {
+        return partiesOf(s) - unarrivedOf(s);
+    }
+
+    private static long stateFor(int phase, int parties, int unarrived) {
+        return ((((long) phase) << 32) | (((long) parties) << 16) |
+                (long) unarrived);
+    }
+
+    private static long trippedStateFor(int phase, int parties) {
+        long lp = (long) parties;
+        return (((long) phase) << 32) | (lp << 16) | lp;
+    }
+
+    /**
+     * Returns message string for bad bounds exceptions.
+     */
+    private static String badBounds(int parties, int unarrived) {
+        return ("Attempt to set " + unarrived +
+                " unarrived of " + parties + " parties");
+    }
+
+    /**
+     * The parent of this phaser, or null if none
+     */
+    private final Phaser parent;
+
+    /**
+     * The root of phaser tree. Equals this if not in a tree.  Used to
+     * support faster state push-down.
+     */
+    private final Phaser root;
+
+    // Wait queues
+
+    /**
+     * Heads of Treiber stacks for waiting threads. To eliminate
+     * contention while releasing some threads while adding others, we
+     * use two of them, alternating across even and odd phases.
+     */
+    private final AtomicReference<QNode> evenQ = new AtomicReference<QNode>();
+    private final AtomicReference<QNode> oddQ  = new AtomicReference<QNode>();
+
+    private AtomicReference<QNode> queueFor(int phase) {
+        return ((phase & 1) == 0) ? evenQ : oddQ;
+    }
+
+    /**
+     * Returns current state, first resolving lagged propagation from
+     * root if necessary.
+     */
+    private long getReconciledState() {
+        return (parent == null) ? state : reconcileState();
+    }
+
+    /**
+     * Recursively resolves state.
+     */
+    private long reconcileState() {
+        Phaser p = parent;
+        long s = state;
+        if (p != null) {
+            while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) {
+                long parentState = p.getReconciledState();
+                int parentPhase = phaseOf(parentState);
+                int phase = phaseOf(s = state);
+                if (phase != parentPhase) {
+                    long next = trippedStateFor(parentPhase, partiesOf(s));
+                    if (casState(s, next)) {
+                        releaseWaiters(phase);
+                        s = next;
+                    }
+                }
+            }
+        }
+        return s;
+    }
+
+    /**
+     * Creates a new phaser without any initially registered parties,
+     * initial phase number 0, and no parent. Any thread using this
+     * phaser will need to first register for it.
+     */
+    public Phaser() {
+        this(null);
+    }
+
+    /**
+     * Creates a new phaser with the given numbers of registered
+     * unarrived parties, initial phase number 0, and no parent.
+     *
+     * @param parties the number of parties required to trip barrier
+     * @throws IllegalArgumentException if parties less than zero
+     * or greater than the maximum number of parties supported
+     */
+    public Phaser(int parties) {
+        this(null, parties);
+    }
+
+    /**
+     * Creates a new phaser with the given parent, without any
+     * initially registered parties. If parent is non-null this phaser
+     * is registered with the parent and its initial phase number is
+     * the same as that of parent phaser.
+     *
+     * @param parent the parent phaser
+     */
+    public Phaser(Phaser parent) {
+        int phase = 0;
+        this.parent = parent;
+        if (parent != null) {
+            this.root = parent.root;
+            phase = parent.register();
+        }
+        else
+            this.root = this;
+        this.state = trippedStateFor(phase, 0);
+    }
+
+    /**
+     * Creates a new phaser with the given parent and numbers of
+     * registered unarrived parties. If parent is non-null, this phaser
+     * is registered with the parent and its initial phase number is
+     * the same as that of parent phaser.
+     *
+     * @param parent the parent phaser
+     * @param parties the number of parties required to trip barrier
+     * @throws IllegalArgumentException if parties less than zero
+     * or greater than the maximum number of parties supported
+     */
+    public Phaser(Phaser parent, int parties) {
+        if (parties < 0 || parties > ushortMask)
+            throw new IllegalArgumentException("Illegal number of parties");
+        int phase = 0;
+        this.parent = parent;
+        if (parent != null) {
+            this.root = parent.root;
+            phase = parent.register();
+        }
+        else
+            this.root = this;
+        this.state = trippedStateFor(phase, parties);
+    }
+
+    /**
+     * Adds a new unarrived party to this phaser.
+     *
+     * @return the arrival phase number to which this registration applied
+     * @throws IllegalStateException if attempting to register more
+     * than the maximum supported number of parties
+     */
+    public int register() {
+        return doRegister(1);
+    }
+
+    /**
+     * Adds the given number of new unarrived parties to this phaser.
+     *
+     * @param parties the number of parties required to trip barrier
+     * @return the arrival phase number to which this registration applied
+     * @throws IllegalStateException if attempting to register more
+     * than the maximum supported number of parties
+     */
+    public int bulkRegister(int parties) {
+        if (parties < 0)
+            throw new IllegalArgumentException();
+        if (parties == 0)
+            return getPhase();
+        return doRegister(parties);
+    }
+
+    /**
+     * Shared code for register, bulkRegister
+     */
+    private int doRegister(int registrations) {
+        int phase;
+        for (;;) {
+            long s = getReconciledState();
+            phase = phaseOf(s);
+            int unarrived = unarrivedOf(s) + registrations;
+            int parties = partiesOf(s) + registrations;
+            if (phase < 0)
+                break;
+            if (parties > ushortMask || unarrived > ushortMask)
+                throw new IllegalStateException(badBounds(parties, unarrived));
+            if (phase == phaseOf(root.state) &&
+                casState(s, stateFor(phase, parties, unarrived)))
+                break;
+        }
+        return phase;
+    }
+
+    /**
+     * Arrives at the barrier, but does not wait for others.  (You can
+     * in turn wait for others via {@link #awaitAdvance}).  It is an
+     * unenforced usage error for an unregistered party to invoke this
+     * method.
+     *
+     * @return the arrival phase number, or a negative value if terminated
+     * @throws IllegalStateException if not terminated and the number
+     * of unarrived parties would become negative
+     */
+    public int arrive() {
+        int phase;
+        for (;;) {
+            long s = state;
+            phase = phaseOf(s);
+            if (phase < 0)
+                break;
+            int parties = partiesOf(s);
+            int unarrived = unarrivedOf(s) - 1;
+            if (unarrived > 0) {        // Not the last arrival
+                if (casState(s, s - 1)) // s-1 adds one arrival
+                    break;
+            }
+            else if (unarrived == 0) {  // the last arrival
+                Phaser par = parent;
+                if (par == null) {      // directly trip
+                    if (casState
+                        (s,
+                         trippedStateFor(onAdvance(phase, parties) ? -1 :
+                                         ((phase + 1) & phaseMask), parties))) {
+                        releaseWaiters(phase);
+                        break;
+                    }
+                }
+                else {                  // cascade to parent
+                    if (casState(s, s - 1)) { // zeroes unarrived
+                        par.arrive();
+                        reconcileState();
+                        break;
+                    }
+                }
+            }
+            else if (phase != phaseOf(root.state)) // or if unreconciled
+                reconcileState();
+            else
+                throw new IllegalStateException(badBounds(parties, unarrived));
+        }
+        return phase;
+    }
+
+    /**
+     * Arrives at the barrier and deregisters from it without waiting
+     * for others. Deregistration reduces the number of parties
+     * required to trip the barrier in future phases.  If this phaser
+     * has a parent, and deregistration causes this phaser to have
+     * zero parties, this phaser also arrives at and is deregistered
+     * from its parent.  It is an unenforced usage error for an
+     * unregistered party to invoke this method.
+     *
+     * @return the arrival phase number, or a negative value if terminated
+     * @throws IllegalStateException if not terminated and the number
+     * of registered or unarrived parties would become negative
+     */
+    public int arriveAndDeregister() {
+        // similar code to arrive, but too different to merge
+        Phaser par = parent;
+        int phase;
+        for (;;) {
+            long s = state;
+            phase = phaseOf(s);
+            if (phase < 0)
+                break;
+            int parties = partiesOf(s) - 1;
+            int unarrived = unarrivedOf(s) - 1;
+            if (parties >= 0) {
+                if (unarrived > 0 || (unarrived == 0 && par != null)) {
+                    if (casState
+                        (s,
+                         stateFor(phase, parties, unarrived))) {
+                        if (unarrived == 0) {
+                            par.arriveAndDeregister();
+                            reconcileState();
+                        }
+                        break;
+                    }
+                    continue;
+                }
+                if (unarrived == 0) {
+                    if (casState
+                        (s,
+                         trippedStateFor(onAdvance(phase, parties) ? -1 :
+                                         ((phase + 1) & phaseMask), parties))) {
+                        releaseWaiters(phase);
+                        break;
+                    }
+                    continue;
+                }
+                if (par != null && phase != phaseOf(root.state)) {
+                    reconcileState();
+                    continue;
+                }
+            }
+            throw new IllegalStateException(badBounds(parties, unarrived));
+        }
+        return phase;
+    }
+
+    /**
+     * Arrives at the barrier and awaits others. Equivalent in effect
+     * to {@code awaitAdvance(arrive())}.  If you need to await with
+     * interruption or timeout, you can arrange this with an analogous
+     * construction using one of the other forms of the awaitAdvance
+     * method.  If instead you need to deregister upon arrival use
+     * {@code arriveAndDeregister}. It is an unenforced usage error
+     * for an unregistered party to invoke this method.
+     *
+     * @return the arrival phase number, or a negative number if terminated
+     * @throws IllegalStateException if not terminated and the number
+     * of unarrived parties would become negative
+     */
+    public int arriveAndAwaitAdvance() {
+        return awaitAdvance(arrive());
+    }
+
+    /**
+     * Awaits the phase of the barrier to advance from the given phase
+     * value, returning immediately if the current phase of the
+     * barrier is not equal to the given phase value or this barrier
+     * is terminated.  It is an unenforced usage error for an
+     * unregistered party to invoke this method.
+     *
+     * @param phase an arrival phase number, or negative value if
+     * terminated; this argument is normally the value returned by a
+     * previous call to {@code arrive} or its variants
+     * @return the next arrival phase number, or a negative value
+     * if terminated or argument is negative
+     */
+    public int awaitAdvance(int phase) {
+        if (phase < 0)
+            return phase;
+        long s = getReconciledState();
+        int p = phaseOf(s);
+        if (p != phase)
+            return p;
+        if (unarrivedOf(s) == 0 && parent != null)
+            parent.awaitAdvance(phase);
+        // Fall here even if parent waited, to reconcile and help release
+        return untimedWait(phase);
+    }
+
+    /**
+     * Awaits the phase of the barrier to advance from the given phase
+     * value, throwing {@code InterruptedException} if interrupted
+     * while waiting, or returning immediately if the current phase of
+     * the barrier is not equal to the given phase value or this
+     * barrier is terminated. It is an unenforced usage error for an
+     * unregistered party to invoke this method.
+     *
+     * @param phase an arrival phase number, or negative value if
+     * terminated; this argument is normally the value returned by a
+     * previous call to {@code arrive} or its variants
+     * @return the next arrival phase number, or a negative value
+     * if terminated or argument is negative
+     * @throws InterruptedException if thread interrupted while waiting
+     */
+    public int awaitAdvanceInterruptibly(int phase)
+        throws InterruptedException {
+        if (phase < 0)
+            return phase;
+        long s = getReconciledState();
+        int p = phaseOf(s);
+        if (p != phase)
+            return p;
+        if (unarrivedOf(s) == 0 && parent != null)
+            parent.awaitAdvanceInterruptibly(phase);
+        return interruptibleWait(phase);
+    }
+
+    /**
+     * Awaits the phase of the barrier to advance from the given phase
+     * value or the given timeout to elapse, throwing {@code
+     * InterruptedException} if interrupted while waiting, or
+     * returning immediately if the current phase of the barrier is
+     * not equal to the given phase value or this barrier is
+     * terminated.  It is an unenforced usage error for an
+     * unregistered party to invoke this method.
+     *
+     * @param phase an arrival phase number, or negative value if
+     * terminated; this argument is normally the value returned by a
+     * previous call to {@code arrive} or its variants
+     * @param timeout how long to wait before giving up, in units of
+     *        {@code unit}
+     * @param unit a {@code TimeUnit} determining how to interpret the
+     *        {@code timeout} parameter
+     * @return the next arrival phase number, or a negative value
+     * if terminated or argument is negative
+     * @throws InterruptedException if thread interrupted while waiting
+     * @throws TimeoutException if timed out while waiting
+     */
+    public int awaitAdvanceInterruptibly(int phase,
+                                         long timeout, TimeUnit unit)
+        throws InterruptedException, TimeoutException {
+        if (phase < 0)
+            return phase;
+        long s = getReconciledState();
+        int p = phaseOf(s);
+        if (p != phase)
+            return p;
+        if (unarrivedOf(s) == 0 && parent != null)
+            parent.awaitAdvanceInterruptibly(phase, timeout, unit);
+        return timedWait(phase, unit.toNanos(timeout));
+    }
+
+    /**
+     * Forces this barrier to enter termination state. Counts of
+     * arrived and registered parties are unaffected. If this phaser
+     * has a parent, it too is terminated. This method may be useful
+     * for coordinating recovery after one or more tasks encounter
+     * unexpected exceptions.
+     */
+    public void forceTermination() {
+        for (;;) {
+            long s = getReconciledState();
+            int phase = phaseOf(s);
+            int parties = partiesOf(s);
+            int unarrived = unarrivedOf(s);
+            if (phase < 0 ||
+                casState(s, stateFor(-1, parties, unarrived))) {
+                releaseWaiters(0);
+                releaseWaiters(1);
+                if (parent != null)
+                    parent.forceTermination();
+                return;
+            }
+        }
+    }
+
+    /**
+     * Returns the current phase number. The maximum phase number is
+     * {@code Integer.MAX_VALUE}, after which it restarts at
+     * zero. Upon termination, the phase number is negative.
+     *
+     * @return the phase number, or a negative value if terminated
+     */
+    public final int getPhase() {
+        return phaseOf(getReconciledState());
+    }
+
+    /**
+     * Returns the number of parties registered at this barrier.
+     *
+     * @return the number of parties
+     */
+    public int getRegisteredParties() {
+        return partiesOf(state);
+    }
+
+    /**
+     * Returns the number of registered parties that have arrived at
+     * the current phase of this barrier.
+     *
+     * @return the number of arrived parties
+     */
+    public int getArrivedParties() {
+        return arrivedOf(state);
+    }
+
+    /**
+     * Returns the number of registered parties that have not yet
+     * arrived at the current phase of this barrier.
+     *
+     * @return the number of unarrived parties
+     */
+    public int getUnarrivedParties() {
+        return unarrivedOf(state);
+    }
+
+    /**
+     * Returns the parent of this phaser, or {@code null} if none.
+     *
+     * @return the parent of this phaser, or {@code null} if none
+     */
+    public Phaser getParent() {
+        return parent;
+    }
+
+    /**
+     * Returns the root ancestor of this phaser, which is the same as
+     * this phaser if it has no parent.
+     *
+     * @return the root ancestor of this phaser
+     */
+    public Phaser getRoot() {
+        return root;
+    }
+
+    /**
+     * Returns {@code true} if this barrier has been terminated.
+     *
+     * @return {@code true} if this barrier has been terminated
+     */
+    public boolean isTerminated() {
+        return getPhase() < 0;
+    }
+
+    /**
+     * Overridable method to perform an action upon impending phase
+     * advance, and to control termination. This method is invoked
+     * upon arrival of the party tripping the barrier (when all other
+     * waiting parties are dormant).  If this method returns {@code
+     * true}, then, rather than advance the phase number, this barrier
+     * will be set to a final termination state, and subsequent calls
+     * to {@link #isTerminated} will return true. Any (unchecked)
+     * Exception or Error thrown by an invocation of this method is
+     * propagated to the party attempting to trip the barrier, in
+     * which case no advance occurs.
+     *
+     * <p>The arguments to this method provide the state of the phaser
+     * prevailing for the current transition. (When called from within
+     * an implementation of {@code onAdvance} the values returned by
+     * methods such as {@code getPhase} may or may not reliably
+     * indicate the state to which this transition applies.)
+     *
+     * <p>The default version returns {@code true} when the number of
+     * registered parties is zero. Normally, overrides that arrange
+     * termination for other reasons should also preserve this
+     * property.
+     *
+     * <p>You may override this method to perform an action with side
+     * effects visible to participating tasks, but it is only sensible
+     * to do so in designs where all parties register before any
+     * arrive, and all {@link #awaitAdvance} at each phase.
+     * Otherwise, you cannot ensure lack of interference from other
+     * parties during the invocation of this method. Additionally,
+     * method {@code onAdvance} may be invoked more than once per
+     * transition if registrations are intermixed with arrivals.
+     *
+     * @param phase the phase number on entering the barrier
+     * @param registeredParties the current number of registered parties
+     * @return {@code true} if this barrier should terminate
+     */
+    protected boolean onAdvance(int phase, int registeredParties) {
+        return registeredParties <= 0;
+    }
+
+    /**
+     * Returns a string identifying this phaser, as well as its
+     * state.  The state, in brackets, includes the String {@code
+     * "phase = "} followed by the phase number, {@code "parties = "}
+     * followed by the number of registered parties, and {@code
+     * "arrived = "} followed by the number of arrived parties.
+     *
+     * @return a string identifying this barrier, as well as its state
+     */
+    public String toString() {
+        long s = getReconciledState();
+        return super.toString() +
+            "[phase = " + phaseOf(s) +
+            " parties = " + partiesOf(s) +
+            " arrived = " + arrivedOf(s) + "]";
+    }
+
+    // methods for waiting
+
+    /**
+     * Wait nodes for Treiber stack representing wait queue
+     */
+    static final class QNode implements ForkJoinPool.ManagedBlocker {
+        final Phaser phaser;
+        final int phase;
+        final long startTime;
+        final long nanos;
+        final boolean timed;
+        final boolean interruptible;
+        volatile boolean wasInterrupted = false;
+        volatile Thread thread; // nulled to cancel wait
+        QNode next;
+        QNode(Phaser phaser, int phase, boolean interruptible,
+              boolean timed, long startTime, long nanos) {
+            this.phaser = phaser;
+            this.phase = phase;
+            this.timed = timed;
+            this.interruptible = interruptible;
+            this.startTime = startTime;
+            this.nanos = nanos;
+            thread = Thread.currentThread();
+        }
+        public boolean isReleasable() {
+            return (thread == null ||
+                    phaser.getPhase() != phase ||
+                    (interruptible && wasInterrupted) ||
+                    (timed && (nanos - (System.nanoTime() - startTime)) <= 0));
+        }
+        public boolean block() {
+            if (Thread.interrupted()) {
+                wasInterrupted = true;
+                if (interruptible)
+                    return true;
+            }
+            if (!timed)
+                LockSupport.park(this);
+            else {
+                long waitTime = nanos - (System.nanoTime() - startTime);
+                if (waitTime <= 0)
+                    return true;
+                LockSupport.parkNanos(this, waitTime);
+            }
+            return isReleasable();
+        }
+        void signal() {
+            Thread t = thread;
+            if (t != null) {
+                thread = null;
+                LockSupport.unpark(t);
+            }
+        }
+        boolean doWait() {
+            if (thread != null) {
+                try {
+                    ForkJoinPool.managedBlock(this, false);
+                } catch (InterruptedException ie) {
+                }
+            }
+            return wasInterrupted;
+        }
+
+    }
+
+    /**
+     * Removes and signals waiting threads from wait queue.
+     */
+    private void releaseWaiters(int phase) {
+        AtomicReference<QNode> head = queueFor(phase);
+        QNode q;
+        while ((q = head.get()) != null) {
+            if (head.compareAndSet(q, q.next))
+                q.signal();
+        }
+    }
+
+    /**
+     * Tries to enqueue given node in the appropriate wait queue.
+     *
+     * @return true if successful
+     */
+    private boolean tryEnqueue(QNode node) {
+        AtomicReference<QNode> head = queueFor(node.phase);
+        return head.compareAndSet(node.next = head.get(), node);
+    }
+
+    /**
+     * Enqueues node and waits unless aborted or signalled.
+     *
+     * @return current phase
+     */
+    private int untimedWait(int phase) {
+        QNode node = null;
+        boolean queued = false;
+        boolean interrupted = false;
+        int p;
+        while ((p = getPhase()) == phase) {
+            if (Thread.interrupted())
+                interrupted = true;
+            else if (node == null)
+                node = new QNode(this, phase, false, false, 0, 0);
+            else if (!queued)
+                queued = tryEnqueue(node);
+            else
+                interrupted = node.doWait();
+        }
+        if (node != null)
+            node.thread = null;
+        releaseWaiters(phase);
+        if (interrupted)
+            Thread.currentThread().interrupt();
+        return p;
+    }
+
+    /**
+     * Interruptible version
+     * @return current phase
+     */
+    private int interruptibleWait(int phase) throws InterruptedException {
+        QNode node = null;
+        boolean queued = false;
+        boolean interrupted = false;
+        int p;
+        while ((p = getPhase()) == phase && !interrupted) {
+            if (Thread.interrupted())
+                interrupted = true;
+            else if (node == null)
+                node = new QNode(this, phase, true, false, 0, 0);
+            else if (!queued)
+                queued = tryEnqueue(node);
+            else
+                interrupted = node.doWait();
+        }
+        if (node != null)
+            node.thread = null;
+        if (p != phase || (p = getPhase()) != phase)
+            releaseWaiters(phase);
+        if (interrupted)
+            throw new InterruptedException();
+        return p;
+    }
+
+    /**
+     * Timeout version.
+     * @return current phase
+     */
+    private int timedWait(int phase, long nanos)
+        throws InterruptedException, TimeoutException {
+        long startTime = System.nanoTime();
+        QNode node = null;
+        boolean queued = false;
+        boolean interrupted = false;
+        int p;
+        while ((p = getPhase()) == phase && !interrupted) {
+            if (Thread.interrupted())
+                interrupted = true;
+            else if (nanos - (System.nanoTime() - startTime) <= 0)
+                break;
+            else if (node == null)
+                node = new QNode(this, phase, true, true, startTime, nanos);
+            else if (!queued)
+                queued = tryEnqueue(node);
+            else
+                interrupted = node.doWait();
+        }
+        if (node != null)
+            node.thread = null;
+        if (p != phase || (p = getPhase()) != phase)
+            releaseWaiters(phase);
+        if (interrupted)
+            throw new InterruptedException();
+        if (p == phase)
+            throw new TimeoutException();
+        return p;
+    }
+
+    // Unsafe mechanics
+
+    private static final sun.misc.Unsafe UNSAFE = sun.misc.Unsafe.getUnsafe();
+    private static final long stateOffset =
+        objectFieldOffset("state", Phaser.class);
+
+    private final boolean casState(long cmp, long val) {
+        return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
+    }
+
+    private static long objectFieldOffset(String field, Class<?> klazz) {
+        try {
+            return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
+        } catch (NoSuchFieldException e) {
+            // Convert Exception to corresponding Error
+            NoSuchFieldError error = new NoSuchFieldError(field);
+            error.initCause(e);
+            throw error;
+        }
+    }
+}

src/share/classes/java/util/concurrent/RecursiveAction.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+/**
+ * A recursive resultless {@link ForkJoinTask}.  This class
+ * establishes conventions to parameterize resultless actions as
+ * {@code Void} {@code ForkJoinTask}s. Because {@code null} is the
+ * only valid value of type {@code Void}, methods such as join always
+ * return {@code null} upon completion.
+ *
+ * <p><b>Sample Usages.</b> Here is a sketch of a ForkJoin sort that
+ * sorts a given {@code long[]} array:
+ *
+ *  <pre> {@code
+ * class SortTask extends RecursiveAction {
+ *   final long[] array; final int lo; final int hi;
+ *   SortTask(long[] array, int lo, int hi) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *   }
+ *   protected void compute() {
+ *     if (hi - lo < THRESHOLD)
+ *       sequentiallySort(array, lo, hi);
+ *     else {
+ *       int mid = (lo + hi) >>> 1;
+ *       invokeAll(new SortTask(array, lo, mid),
+ *                 new SortTask(array, mid, hi));
+ *       merge(array, lo, hi);
+ *     }
+ *   }
+ * }}</pre>
+ *
+ * You could then sort {@code anArray} by creating {@code new
+ * SortTask(anArray, 0, anArray.length-1) } and invoking it in a
+ * ForkJoinPool.  As a more concrete simple example, the following
+ * task increments each element of an array:
+ *  <pre> {@code
+ * class IncrementTask extends RecursiveAction {
+ *   final long[] array; final int lo; final int hi;
+ *   IncrementTask(long[] array, int lo, int hi) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *   }
+ *   protected void compute() {
+ *     if (hi - lo < THRESHOLD) {
+ *       for (int i = lo; i < hi; ++i)
+ *         array[i]++;
+ *     }
+ *     else {
+ *       int mid = (lo + hi) >>> 1;
+ *       invokeAll(new IncrementTask(array, lo, mid),
+ *                 new IncrementTask(array, mid, hi));
+ *     }
+ *   }
+ * }}</pre>
+ *
+ * <p>The following example illustrates some refinements and idioms
+ * that may lead to better performance: RecursiveActions need not be
+ * fully recursive, so long as they maintain the basic
+ * divide-and-conquer approach. Here is a class that sums the squares
+ * of each element of a double array, by subdividing out only the
+ * right-hand-sides of repeated divisions by two, and keeping track of
+ * them with a chain of {@code next} references. It uses a dynamic
+ * threshold based on method {@code getSurplusQueuedTaskCount}, but
+ * counterbalances potential excess partitioning by directly
+ * performing leaf actions on unstolen tasks rather than further
+ * subdividing.
+ *
+ *  <pre> {@code
+ * double sumOfSquares(ForkJoinPool pool, double[] array) {
+ *   int n = array.length;
+ *   Applyer a = new Applyer(array, 0, n, null);
+ *   pool.invoke(a);
+ *   return a.result;
+ * }
+ *
+ * class Applyer extends RecursiveAction {
+ *   final double[] array;
+ *   final int lo, hi;
+ *   double result;
+ *   Applyer next; // keeps track of right-hand-side tasks
+ *   Applyer(double[] array, int lo, int hi, Applyer next) {
+ *     this.array = array; this.lo = lo; this.hi = hi;
+ *     this.next = next;
+ *   }
+ *
+ *   double atLeaf(int l, int h) {
+ *     double sum = 0;
+ *     for (int i = l; i < h; ++i) // perform leftmost base step
+ *       sum += array[i] * array[i];
+ *     return sum;
+ *   }
+ *
+ *   protected void compute() {
+ *     int l = lo;
+ *     int h = hi;
+ *     Applyer right = null;
+ *     while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) {
+ *        int mid = (l + h) >>> 1;
+ *        right = new Applyer(array, mid, h, right);
+ *        right.fork();
+ *        h = mid;
+ *     }
+ *     double sum = atLeaf(l, h);
+ *     while (right != null) {
+ *        if (right.tryUnfork()) // directly calculate if not stolen
+ *          sum += right.atLeaf(right.lo, right.hi);
+ *       else {
+ *          right.helpJoin();
+ *          sum += right.result;
+ *        }
+ *        right = right.next;
+ *      }
+ *     result = sum;
+ *   }
+ * }}</pre>
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class RecursiveAction extends ForkJoinTask<Void> {
+    private static final long serialVersionUID = 5232453952276485070L;
+
+    /**
+     * The main computation performed by this task.
+     */
+    protected abstract void compute();
+
+    /**
+     * Always returns null.
+     */
+    public final Void getRawResult() { return null; }
+
+    /**
+     * Requires null completion value.
+     */
+    protected final void setRawResult(Void mustBeNull) { }
+
+    /**
+     * Implements execution conventions for RecursiveActions.
+     */
+    protected final boolean exec() {
+        compute();
+        return true;
+    }
+
+}

src/share/classes/java/util/concurrent/RecursiveTask.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+/**
+ * A recursive result-bearing {@link ForkJoinTask}.
+ *
+ * <p>For a classic example, here is a task computing Fibonacci numbers:
+ *
+ *  <pre> {@code
+ * class Fibonacci extends RecursiveTask<Integer> {
+ *   final int n;
+ *   Fibonacci(int n) { this.n = n; }
+ *   Integer compute() {
+ *     if (n <= 1)
+ *        return n;
+ *     Fibonacci f1 = new Fibonacci(n - 1);
+ *     f1.fork();
+ *     Fibonacci f2 = new Fibonacci(n - 2);
+ *     return f2.compute() + f1.join();
+ *   }
+ * }}</pre>
+ *
+ * However, besides being a dumb way to compute Fibonacci functions
+ * (there is a simple fast linear algorithm that you'd use in
+ * practice), this is likely to perform poorly because the smallest
+ * subtasks are too small to be worthwhile splitting up. Instead, as
+ * is the case for nearly all fork/join applications, you'd pick some
+ * minimum granularity size (for example 10 here) for which you always
+ * sequentially solve rather than subdividing.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
+    private static final long serialVersionUID = 5232453952276485270L;
+
+    /**
+     * The result of the computation.
+     */
+    V result;
+
+    /**
+     * The main computation performed by this task.
+     */
+    protected abstract V compute();
+
+    public final V getRawResult() {
+        return result;
+    }
+
+    protected final void setRawResult(V value) {
+        result = value;
+    }
+
+    /**
+     * Implements execution conventions for RecursiveTask.
+     */
+    protected final boolean exec() {
+        result = compute();
+        return true;
+    }
+
+}

src/share/classes/java/util/concurrent/ScheduledThreadPoolExecutor.java

@@ -61,6 +61,14 @@ import java.util.*;
  * causes tasks to be immediately removed from the work queue at
  * time of cancellation.
  *
+ * <p>Successive executions of a task scheduled via
+ * <code>scheduleAtFixedRate</code> or
+ * <code>scheduleWithFixedDelay</code> do not overlap. While different
+ * executions may be performed by different threads, the effects of
+ * prior executions <a
+ * href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
+ * those of subsequent ones.
+ *
  * <p>While this class inherits from {@link ThreadPoolExecutor}, a few
  * of the inherited tuning methods are not useful for it. In
  * particular, because it acts as a fixed-sized pool using

src/share/classes/java/util/concurrent/ThreadLocalRandom.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+import java.util.Random;
+
+/**
+ * A random number generator isolated to the current thread.  Like the
+ * global {@link java.util.Random} generator used by the {@link
+ * java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
+ * with an internally generated seed that may not otherwise be
+ * modified. When applicable, use of {@code ThreadLocalRandom} rather
+ * than shared {@code Random} objects in concurrent programs will
+ * typically encounter much less overhead and contention.  Use of
+ * {@code ThreadLocalRandom} is particularly appropriate when multiple
+ * tasks (for example, each a {@link ForkJoinTask}) use random numbers
+ * in parallel in thread pools.
+ *
+ * <p>Usages of this class should typically be of the form:
+ * {@code ThreadLocalRandom.current().nextX(...)} (where
+ * {@code X} is {@code Int}, {@code Long}, etc).
+ * When all usages are of this form, it is never possible to
+ * accidently share a {@code ThreadLocalRandom} across multiple threads.
+ *
+ * <p>This class also provides additional commonly used bounded random
+ * generation methods.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ */
+public class ThreadLocalRandom extends Random {
+    // same constants as Random, but must be redeclared because private
+    private final static long multiplier = 0x5DEECE66DL;
+    private final static long addend = 0xBL;
+    private final static long mask = (1L << 48) - 1;
+
+    /**
+     * The random seed. We can't use super.seed.
+     */
+    private long rnd;
+
+    /**
+     * Initialization flag to permit the first and only allowed call
+     * to setSeed (inside Random constructor) to succeed.  We can't
+     * allow others since it would cause setting seed in one part of a
+     * program to unintentionally impact other usages by the thread.
+     */
+    boolean initialized;
+
+    // Padding to help avoid memory contention among seed updates in
+    // different TLRs in the common case that they are located near
+    // each other.
+    private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
+
+    /**
+     * The actual ThreadLocal
+     */
+    private static final ThreadLocal<ThreadLocalRandom> localRandom =
+        new ThreadLocal<ThreadLocalRandom>() {
+            protected ThreadLocalRandom initialValue() {
+                return new ThreadLocalRandom();
+            }
+    };
+
+
+    /**
+     * Constructor called only by localRandom.initialValue.
+     * We rely on the fact that the superclass no-arg constructor
+     * invokes setSeed exactly once to initialize.
+     */
+    ThreadLocalRandom() {
+        super();
+    }
+
+    /**
+     * Returns the current thread's {@code ThreadLocalRandom}.
+     *
+     * @return the current thread's {@code ThreadLocalRandom}
+     */
+    public static ThreadLocalRandom current() {
+        return localRandom.get();
+    }
+
+    /**
+     * Throws {@code UnsupportedOperationException}.  Setting seeds in
+     * this generator is not supported.
+     *
+     * @throws UnsupportedOperationException always
+     */
+    public void setSeed(long seed) {
+        if (initialized)
+            throw new UnsupportedOperationException();
+        initialized = true;
+        rnd = (seed ^ multiplier) & mask;
+    }
+
+    protected int next(int bits) {
+        rnd = (rnd * multiplier + addend) & mask;
+        return (int) (rnd >>> (48-bits));
+    }
+
+    /**
+     * Returns a pseudorandom, uniformly distributed value between the
+     * given least value (inclusive) and bound (exclusive).
+     *
+     * @param least the least value returned
+     * @param bound the upper bound (exclusive)
+     * @throws IllegalArgumentException if least greater than or equal
+     * to bound
+     * @return the next value
+     */
+    public int nextInt(int least, int bound) {
+        if (least >= bound)
+            throw new IllegalArgumentException();
+        return nextInt(bound - least) + least;
+    }
+
+    /**
+     * Returns a pseudorandom, uniformly distributed value
+     * between 0 (inclusive) and the specified value (exclusive).
+     *
+     * @param n the bound on the random number to be returned.  Must be
+     *        positive.
+     * @return the next value
+     * @throws IllegalArgumentException if n is not positive
+     */
+    public long nextLong(long n) {
+        if (n <= 0)
+            throw new IllegalArgumentException("n must be positive");
+        // Divide n by two until small enough for nextInt. On each
+        // iteration (at most 31 of them but usually much less),
+        // randomly choose both whether to include high bit in result
+        // (offset) and whether to continue with the lower vs upper
+        // half (which makes a difference only if odd).
+        long offset = 0;
+        while (n >= Integer.MAX_VALUE) {
+            int bits = next(2);
+            long half = n >>> 1;
+            long nextn = ((bits & 2) == 0) ? half : n - half;
+            if ((bits & 1) == 0)
+                offset += n - nextn;
+            n = nextn;
+        }
+        return offset + nextInt((int) n);
+    }
+
+    /**
+     * Returns a pseudorandom, uniformly distributed value between the
+     * given least value (inclusive) and bound (exclusive).
+     *
+     * @param least the least value returned
+     * @param bound the upper bound (exclusive)
+     * @return the next value
+     * @throws IllegalArgumentException if least greater than or equal
+     * to bound
+     */
+    public long nextLong(long least, long bound) {
+        if (least >= bound)
+            throw new IllegalArgumentException();
+        return nextLong(bound - least) + least;
+    }
+
+    /**
+     * Returns a pseudorandom, uniformly distributed {@code double} value
+     * between 0 (inclusive) and the specified value (exclusive).
+     *
+     * @param n the bound on the random number to be returned.  Must be
+     *        positive.
+     * @return the next value
+     * @throws IllegalArgumentException if n is not positive
+     */
+    public double nextDouble(double n) {
+        if (n <= 0)
+            throw new IllegalArgumentException("n must be positive");
+        return nextDouble() * n;
+    }
+
+    /**
+     * Returns a pseudorandom, uniformly distributed value between the
+     * given least value (inclusive) and bound (exclusive).
+     *
+     * @param least the least value returned
+     * @param bound the upper bound (exclusive)
+     * @return the next value
+     * @throws IllegalArgumentException if least greater than or equal
+     * to bound
+     */
+    public double nextDouble(double least, double bound) {
+        if (least >= bound)
+            throw new IllegalArgumentException();
+        return nextDouble() * (bound - least) + least;
+    }
+
+    private static final long serialVersionUID = -5851777807851030925L;
+}

src/share/classes/java/util/concurrent/TransferQueue.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+package java.util.concurrent;
+
+/**
+ * A {@link BlockingQueue} in which producers may wait for consumers
+ * to receive elements.  A {@code TransferQueue} may be useful for
+ * example in message passing applications in which producers
+ * sometimes (using method {@link #transfer}) await receipt of
+ * elements by consumers invoking {@code take} or {@code poll}, while
+ * at other times enqueue elements (via method {@code put}) without
+ * waiting for receipt.
+ * {@linkplain #tryTransfer(Object) Non-blocking} and
+ * {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
+ * {@code tryTransfer} are also available.
+ * A {@code TransferQueue} may also be queried, via {@link
+ * #hasWaitingConsumer}, whether there are any threads waiting for
+ * items, which is a converse analogy to a {@code peek} operation.
+ *
+ * <p>Like other blocking queues, a {@code TransferQueue} may be
+ * capacity bounded.  If so, an attempted transfer operation may
+ * initially block waiting for available space, and/or subsequently
+ * block waiting for reception by a consumer.  Note that in a queue
+ * with zero capacity, such as {@link SynchronousQueue}, {@code put}
+ * and {@code transfer} are effectively synonymous.
+ *
+ * <p>This interface is a member of the
+ * <a href="{@docRoot}/../technotes/guides/collections/index.html">
+ * Java Collections Framework</a>.
+ *
+ * @since 1.7
+ * @author Doug Lea
+ * @param <E> the type of elements held in this collection
+ */
+public interface TransferQueue<E> extends BlockingQueue<E> {
+    /**
+     * Transfers the element to a waiting consumer immediately, if possible.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * otherwise returning {@code false} without enqueuing the element.
+     *
+     * @param e the element to transfer
+     * @return {@code true} if the element was transferred, else
+     *         {@code false}
+     * @throws ClassCastException if the class of the specified element
+     *         prevents it from being added to this queue
+     * @throws NullPointerException if the specified element is null
+     * @throws IllegalArgumentException if some property of the specified
+     *         element prevents it from being added to this queue
+     */
+    boolean tryTransfer(E e);
+
+    /**
+     * Transfers the element to a consumer, waiting if necessary to do so.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * else waits until the element is received by a consumer.
+     *
+     * @param e the element to transfer
+     * @throws InterruptedException if interrupted while waiting,
+     *         in which case the element is not left enqueued
+     * @throws ClassCastException if the class of the specified element
+     *         prevents it from being added to this queue
+     * @throws NullPointerException if the specified element is null
+     * @throws IllegalArgumentException if some property of the specified
+     *         element prevents it from being added to this queue
+     */
+    void transfer(E e) throws InterruptedException;
+
+    /**
+     * Transfers the element to a consumer if it is possible to do so
+     * before the timeout elapses.
+     *
+     * <p>More precisely, transfers the specified element immediately
+     * if there exists a consumer already waiting to receive it (in
+     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
+     * else waits until the element is received by a consumer,
+     * returning {@code false} if the specified wait time elapses
+     * before the element can be transferred.
+     *
+     * @param e the element to transfer
+     * @param timeout how long to wait before giving up, in units of
+     *        {@code unit}
+     * @param unit a {@code TimeUnit} determining how to interpret the
+     *        {@code timeout} parameter
+     * @return {@code true} if successful, or {@code false} if
+     *         the specified waiting time elapses before completion,
+     *         in which case the element is not left enqueued
+     * @throws InterruptedException if interrupted while waiting,
+     *         in which case the element is not left enqueued
+     * @throws ClassCastException if the class of the specified element
+     *         prevents it from being added to this queue
+     * @throws NullPointerException if the specified element is null
+     * @throws IllegalArgumentException if some property of the specified
+     *         element prevents it from being added to this queue
+     */
+    boolean tryTransfer(E e, long timeout, TimeUnit unit)
+        throws InterruptedException;
+
+    /**
+     * Returns {@code true} if there is at least one consumer waiting
+     * to receive an element via {@link #take} or
+     * timed {@link #poll(long,TimeUnit) poll}.
+     * The return value represents a momentary state of affairs.
+     *
+     * @return {@code true} if there is at least one waiting consumer
+     */
+    boolean hasWaitingConsumer();
+
+    /**
+     * Returns an estimate of the number of consumers waiting to
+     * receive elements via {@link #take} or timed
+     * {@link #poll(long,TimeUnit) poll}.  The return value is an
+     * approximation of a momentary state of affairs, that may be
+     * inaccurate if consumers have completed or given up waiting.
+     * The value may be useful for monitoring and heuristics, but
+     * not for synchronization control.  Implementations of this
+     * method are likely to be noticeably slower than those for
+     * {@link #hasWaitingConsumer}.
+     *
+     * @return the number of consumers waiting to receive elements
+     */
+    int getWaitingConsumerCount();
+}

src/share/classes/java/util/concurrent/locks/Condition.java

@@ -170,8 +170,8 @@ import java.util.Date;
  * <p>As interruption generally implies cancellation, and checks for
  * interruption are often infrequent, an implementation can favor responding
  * to an interrupt over normal method return. This is true even if it can be
- * shown that the interrupt occurred after another action may have unblocked
- * the thread. An implementation should document this behavior.
+ * shown that the interrupt occurred after another action that may have
+ * unblocked the thread. An implementation should document this behavior.
  *
  * @since 1.5
  * @author Doug Lea

src/share/classes/java/util/concurrent/package-info.java

@@ -92,6 +92,13 @@
  * assists in coordinating the processing of groups of
  * asynchronous tasks.
  *
+ * <p>Class {@link java.util.concurrent.ForkJoinPool} provides an
+ * Executor primarily designed for processing instances of {@link
+ * java.util.concurrent.ForkJoinTask} and its subclasses.  These
+ * classes employ a work-stealing scheduler that attains high
+ * throughput for tasks conforming to restrictions that often hold in
+ * computation-intensive parallel processing.
+ *
  * <h2>Queues</h2>
  *
  * The {@link java.util.concurrent.ConcurrentLinkedQueue} class
@@ -110,6 +117,12 @@
  * for producer-consumer, messaging, parallel tasking, and
  * related concurrent designs.
  *
+ * <p> Extended interface {@link java.util.concurrent.TransferQueue},
+ * and implementation {@link java.util.concurrent.LinkedTransferQueue}
+ * introduce a synchronous {@code transfer} method (along with related
+ * features) in which a producer may optionally block awaiting its
+ * consumer.
+ *
  * <p>The {@link java.util.concurrent.BlockingDeque} interface
  * extends {@code BlockingQueue} to support both FIFO and LIFO
  * (stack-based) operations.
@@ -136,15 +149,28 @@
  *
  * <h2>Synchronizers</h2>
  *
- * Four classes aid common special-purpose synchronization idioms.
- * {@link java.util.concurrent.Semaphore} is a classic concurrency tool.
- * {@link java.util.concurrent.CountDownLatch} is a very simple yet very
- * common utility for blocking until a given number of signals, events,
- * or conditions hold.  A {@link java.util.concurrent.CyclicBarrier} is a
- * resettable multiway synchronization point useful in some styles of
- * parallel programming.  An {@link java.util.concurrent.Exchanger} allows
- * two threads to exchange objects at a rendezvous point, and is useful
- * in several pipeline designs.
+ * Five classes aid common special-purpose synchronization idioms.
+ * <ul>
+ *
+ * <li>{@link java.util.concurrent.Semaphore} is a classic concurrency tool.
+ *
+ * <li>{@link java.util.concurrent.CountDownLatch} is a very simple yet
+ * very common utility for blocking until a given number of signals,
+ * events, or conditions hold.
+ *
+ * <li>A {@link java.util.concurrent.CyclicBarrier} is a resettable
+ * multiway synchronization point useful in some styles of parallel
+ * programming.
+ *
+ * <li>A {@link java.util.concurrent.Phaser} provides
+ * a more flexible form of barrier that may be used to control phased
+ * computation among multiple threads.
+ *
+ * <li>An {@link java.util.concurrent.Exchanger} allows two threads to
+ * exchange objects at a rendezvous point, and is useful in several
+ * pipeline designs.
+ *
+ * </ul>
  *
  * <h2>Concurrent Collections</h2>
  *
@@ -259,7 +285,8 @@
  *   in each thread <i>happen-before</i> those subsequent to the
  *   corresponding {@code exchange()} in another thread.
  *
- *   <li>Actions prior to calling {@code CyclicBarrier.await}
+ *   <li>Actions prior to calling {@code CyclicBarrier.await} and
+ *   {@code Phaser.awaitAdvance} (as well as its variants)
  *   <i>happen-before</i> actions performed by the barrier action, and
  *   actions performed by the barrier action <i>happen-before</i> actions
  *   subsequent to a successful return from the corresponding {@code await}

test/java/util/Collection/BiggernYours.java

@@ -178,10 +178,10 @@ public class BiggernYours {
             new ConcurrentLinkedQueue() {
                 public int size() {return randomize(super.size());}});
 
-//         testCollections(
-//             new LinkedTransferQueue(),
-//             new LinkedTransferQueue() {
-//                 public int size() {return randomize(super.size());}});
+        testCollections(
+            new LinkedTransferQueue(),
+            new LinkedTransferQueue() {
+                public int size() {return randomize(super.size());}});
 
         testCollections(
             new LinkedBlockingQueue(),

test/java/util/Collection/IteratorAtEnd.java

@@ -49,7 +49,7 @@ public class IteratorAtEnd {
         testCollection(new LinkedBlockingQueue());
         testCollection(new ArrayBlockingQueue(100));
         testCollection(new ConcurrentLinkedQueue());
-//         testCollection(new LinkedTransferQueue());
+        testCollection(new LinkedTransferQueue());
 
         testMap(new HashMap());
         testMap(new Hashtable());

test/java/util/Collection/MOAT.java

@@ -76,7 +76,7 @@ public class MOAT {
         testCollection(new LinkedBlockingQueue<Integer>(20));
         testCollection(new LinkedBlockingDeque<Integer>(20));
         testCollection(new ConcurrentLinkedQueue<Integer>());
-//         testCollection(new LinkedTransferQueue<Integer>());
+        testCollection(new LinkedTransferQueue<Integer>());
         testCollection(new ConcurrentSkipListSet<Integer>());
         testCollection(Arrays.asList(new Integer(42)));
         testCollection(Arrays.asList(1,2,3));

test/java/util/Collections/CheckedNull.java

@@ -52,7 +52,7 @@ public class CheckedNull {
 
         testMap(Collections.checkedMap(
                     new HashMap<String, String>(),
-                    String.class, String.class));;
+                    String.class, String.class));
     }
 
     ClassCastException cce(F f) {

test/java/util/Collections/RacingCollections.java

@@ -234,7 +234,7 @@ public class RacingCollections {
         List<Queue<Integer>> list =
             new ArrayList<Queue<Integer>>(newConcurrentDeques());
         list.add(new LinkedBlockingQueue<Integer>(10));
-//         list.add(new LinkedTransferQueue<Integer>());
+        list.add(new LinkedTransferQueue<Integer>());
         return list;
     }
 

test/java/util/PriorityQueue/RemoveContains.java

@@ -69,7 +69,7 @@ public class RemoveContains {
         test(new ArrayBlockingQueue<String>(10));
         test(new LinkedBlockingQueue<String>(10));
         test(new LinkedBlockingDeque<String>(10));
-//         test(new LinkedTransferQueue<String>());
+        test(new LinkedTransferQueue<String>());
         test(new ArrayDeque<String>(10));
 
         System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);

test/java/util/concurrent/BlockingQueue/CancelledProducerConsumerLoops.java

@@ -119,12 +119,36 @@ public class CancelledProducerConsumerLoops {
         }
     }
 
+    static final class LTQasSQ<T> extends LinkedTransferQueue<T> {
+        LTQasSQ() { super(); }
+        public void put(T x) {
+            try { super.transfer(x); }
+            catch (InterruptedException ex) { throw new Error(); }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
+    static final class HalfSyncLTQ<T> extends LinkedTransferQueue<T> {
+        HalfSyncLTQ() { super(); }
+        public void put(T x) {
+            if (ThreadLocalRandom.current().nextBoolean())
+                super.put(x);
+            else {
+                try { super.transfer(x); }
+                catch (InterruptedException ex) { throw new Error(); }
+            }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
     static void oneTest(int pairs, int iters) throws Exception {
 
         oneRun(new ArrayBlockingQueue<Integer>(CAPACITY), pairs, iters);
         oneRun(new LinkedBlockingQueue<Integer>(CAPACITY), pairs, iters);
         oneRun(new LinkedBlockingDeque<Integer>(CAPACITY), pairs, iters);
-//         oneRun(new LinkedTransferQueue<Integer>(), pairs, iters);
+        oneRun(new LinkedTransferQueue<Integer>(), pairs, iters);
+        oneRun(new LTQasSQ<Integer>(), pairs, iters);
+        oneRun(new HalfSyncLTQ<Integer>(), pairs, iters);
         oneRun(new SynchronousQueue<Integer>(), pairs, iters / 8);
 
         /* PriorityBlockingQueue is unbounded

test/java/util/concurrent/BlockingQueue/LastElement.java

@@ -37,7 +37,7 @@ public class LastElement {
         testQueue(new LinkedBlockingDeque<Integer>());
         testQueue(new ArrayBlockingQueue<Integer>(10, true));
         testQueue(new ArrayBlockingQueue<Integer>(10, false));
-//         testQueue(new LinkedTransferQueue<Integer>());
+        testQueue(new LinkedTransferQueue<Integer>());
 
         System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
         if (failed > 0) throw new Exception("Some tests failed");

test/java/util/concurrent/BlockingQueue/MultipleProducersSingleConsumerLoops.java

@@ -87,11 +87,35 @@ public class MultipleProducersSingleConsumerLoops {
             throw new Error();
    }
 
+    static final class LTQasSQ<T> extends LinkedTransferQueue<T> {
+        LTQasSQ() { super(); }
+        public void put(T x) {
+            try { super.transfer(x); }
+            catch (InterruptedException ex) { throw new Error(); }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
+    static final class HalfSyncLTQ<T> extends LinkedTransferQueue<T> {
+        HalfSyncLTQ() { super(); }
+        public void put(T x) {
+            if (ThreadLocalRandom.current().nextBoolean())
+                super.put(x);
+            else {
+                try { super.transfer(x); }
+                catch (InterruptedException ex) { throw new Error(); }
+            }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
     static void oneTest(int producers, int iters) throws Exception {
         oneRun(new ArrayBlockingQueue<Integer>(CAPACITY), producers, iters);
         oneRun(new LinkedBlockingQueue<Integer>(CAPACITY), producers, iters);
         oneRun(new LinkedBlockingDeque<Integer>(CAPACITY), producers, iters);
-//         oneRun(new LinkedTransferQueue<Integer>(), producers, iters);
+        oneRun(new LinkedTransferQueue<Integer>(), producers, iters);
+        oneRun(new LTQasSQ<Integer>(), producers, iters);
+        oneRun(new HalfSyncLTQ<Integer>(), producers, iters);
 
         // Don't run PBQ since can legitimately run out of memory
         //        if (print)

test/java/util/concurrent/BlockingQueue/OfferDrainToLoops.java

@@ -63,12 +63,11 @@ public class OfferDrainToLoops {
         test(new LinkedBlockingDeque());
         test(new LinkedBlockingDeque(2000));
         test(new ArrayBlockingQueue(2000));
-//         test(new LinkedTransferQueue());
+        test(new LinkedTransferQueue());
     }
 
     Random getRandom() {
-        return new Random();
-        // return ThreadLocalRandom.current();
+        return ThreadLocalRandom.current();
     }
 
     void test(final BlockingQueue q) throws Throwable {

test/java/util/concurrent/BlockingQueue/PollMemoryLeak.java

@@ -46,7 +46,7 @@ public class PollMemoryLeak {
     public static void main(String[] args) throws InterruptedException {
         final BlockingQueue[] qs = {
             new LinkedBlockingQueue(10),
-//             new LinkedTransferQueue(),
+            new LinkedTransferQueue(),
             new ArrayBlockingQueue(10),
             new SynchronousQueue(),
             new SynchronousQueue(true),

test/java/util/concurrent/BlockingQueue/ProducerConsumerLoops.java

@@ -87,11 +87,35 @@ public class ProducerConsumerLoops {
             throw new Error();
    }
 
+    static final class LTQasSQ<T> extends LinkedTransferQueue<T> {
+        LTQasSQ() { super(); }
+        public void put(T x) {
+            try { super.transfer(x); }
+            catch (InterruptedException ex) { throw new Error(); }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
+    static final class HalfSyncLTQ<T> extends LinkedTransferQueue<T> {
+        HalfSyncLTQ() { super(); }
+        public void put(T x) {
+            if (ThreadLocalRandom.current().nextBoolean())
+                super.put(x);
+            else {
+                try { super.transfer(x); }
+                catch (InterruptedException ex) { throw new Error(); }
+            }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
     static void oneTest(int pairs, int iters) throws Exception {
         oneRun(new ArrayBlockingQueue<Integer>(CAPACITY), pairs, iters);
         oneRun(new LinkedBlockingQueue<Integer>(CAPACITY), pairs, iters);
         oneRun(new LinkedBlockingDeque<Integer>(CAPACITY), pairs, iters);
-//         oneRun(new LinkedTransferQueue<Integer>(), pairs, iters);
+        oneRun(new LinkedTransferQueue<Integer>(), pairs, iters);
+        oneRun(new LTQasSQ<Integer>(), pairs, iters);
+        oneRun(new HalfSyncLTQ<Integer>(), pairs, iters);
         oneRun(new PriorityBlockingQueue<Integer>(), pairs, iters);
         oneRun(new SynchronousQueue<Integer>(), pairs, iters);
 

test/java/util/concurrent/BlockingQueue/SingleProducerMultipleConsumerLoops.java

@@ -73,11 +73,35 @@ public class SingleProducerMultipleConsumerLoops {
             throw new Error();
    }
 
+    static final class LTQasSQ<T> extends LinkedTransferQueue<T> {
+        LTQasSQ() { super(); }
+        public void put(T x) {
+            try { super.transfer(x); }
+            catch (InterruptedException ex) { throw new Error(); }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
+    static final class HalfSyncLTQ<T> extends LinkedTransferQueue<T> {
+        HalfSyncLTQ() { super(); }
+        public void put(T x) {
+            if (ThreadLocalRandom.current().nextBoolean())
+                super.put(x);
+            else {
+                try { super.transfer(x); }
+                catch (InterruptedException ex) { throw new Error(); }
+            }
+        }
+        private final static long serialVersionUID = 42;
+    }
+
     static void oneTest(int consumers, int iters) throws Exception {
         oneRun(new ArrayBlockingQueue<Integer>(CAPACITY), consumers, iters);
         oneRun(new LinkedBlockingQueue<Integer>(CAPACITY), consumers, iters);
         oneRun(new LinkedBlockingDeque<Integer>(CAPACITY), consumers, iters);
-//         oneRun(new LinkedTransferQueue<Integer>(), consumers, iters);
+        oneRun(new LinkedTransferQueue<Integer>(), consumers, iters);
+        oneRun(new LTQasSQ<Integer>(), consumers, iters);
+        oneRun(new HalfSyncLTQ<Integer>(), consumers, iters);
         oneRun(new PriorityBlockingQueue<Integer>(), consumers, iters);
         oneRun(new SynchronousQueue<Integer>(), consumers, iters);
         if (print)

test/java/util/concurrent/ConcurrentQueues/ConcurrentQueueLoops.java

@@ -60,7 +60,7 @@ public class ConcurrentQueueLoops {
         //queues.add(new ArrayBlockingQueue<Integer>(count, true));
         queues.add(new LinkedBlockingQueue<Integer>());
         queues.add(new LinkedBlockingDeque<Integer>());
-//         queues.add(new LinkedTransferQueue<Integer>());
+        queues.add(new LinkedTransferQueue<Integer>());
 
         // Following additional implementations are available from:
         // http://gee.cs.oswego.edu/dl/concurrency-interest/index.html

test/java/util/concurrent/ConcurrentQueues/GCRetention.java

@@ -43,7 +43,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.LinkedBlockingDeque;
 import java.util.concurrent.LinkedBlockingQueue;
-// import java.util.concurrent.LinkedTransferQueue;
+import java.util.concurrent.LinkedTransferQueue;
 import java.util.concurrent.PriorityBlockingQueue;
 import java.util.LinkedList;
 import java.util.PriorityQueue;
@@ -70,7 +70,7 @@ public class GCRetention {
         queues.add(new PriorityBlockingQueue<Boolean>());
         queues.add(new PriorityQueue<Boolean>());
         queues.add(new LinkedList<Boolean>());
-//         queues.add(new LinkedTransferQueue<Boolean>());
+        queues.add(new LinkedTransferQueue<Boolean>());
 
         // Following additional implementations are available from:
         // http://gee.cs.oswego.edu/dl/concurrency-interest/index.html

test/java/util/concurrent/ConcurrentQueues/IteratorWeakConsistency.java

@@ -49,7 +49,7 @@ public class IteratorWeakConsistency {
         test(new LinkedBlockingDeque());
         test(new LinkedBlockingDeque(20));
         test(new ConcurrentLinkedQueue());
-//         test(new LinkedTransferQueue());
+        test(new LinkedTransferQueue());
         // Other concurrent queues (e.g. ArrayBlockingQueue) do not
         // currently have weakly consistent iterators.
         // test(new ArrayBlockingQueue(20));

test/java/util/concurrent/ConcurrentQueues/OfferRemoveLoops.java

@@ -56,12 +56,11 @@ public class OfferRemoveLoops {
         testQueue(new ArrayBlockingQueue(10));
         testQueue(new PriorityBlockingQueue(10));
         testQueue(new ConcurrentLinkedQueue());
-//         testQueue(new LinkedTransferQueue());
+        testQueue(new LinkedTransferQueue());
     }
 
     Random getRandom() {
-        return new Random();
-        // return ThreadLocalRandom.current();
+        return ThreadLocalRandom.current();
     }
 
     void testQueue(final Queue q) throws Throwable {

test/java/util/concurrent/ConcurrentQueues/RemovePollRace.java

@@ -45,7 +45,7 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.LinkedBlockingDeque;
 import java.util.concurrent.LinkedBlockingQueue;
-// import java.util.concurrent.LinkedTransferQueue;
+import java.util.concurrent.LinkedTransferQueue;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -67,7 +67,7 @@ public class RemovePollRace {
         queues.add(new ArrayBlockingQueue<Boolean>(count, true));
         queues.add(new LinkedBlockingQueue<Boolean>());
         queues.add(new LinkedBlockingDeque<Boolean>());
-//         queues.add(new LinkedTransferQueue<Boolean>());
+        queues.add(new LinkedTransferQueue<Boolean>());
 
         // Following additional implementations are available from:
         // http://gee.cs.oswego.edu/dl/concurrency-interest/index.html

test/java/util/concurrent/Phaser/Arrive.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+/*
+ * @test
+ * @bug 6445158
+ * @summary tests for Phaser.arrive()
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Phaser;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class Arrive {
+    void test(String[] args) throws Throwable {
+        final int n = ThreadLocalRandom.current().nextInt(1, 10);
+        final int nthreads = n*3/2;
+        final Phaser startingGate = new Phaser(nthreads);
+        final Phaser phaser = new Phaser(n);
+        final List<Thread> threads = new ArrayList<Thread>();
+        final AtomicInteger count0 = new AtomicInteger(0);
+        final AtomicInteger count1 = new AtomicInteger(0);
+        final Runnable task = new Runnable() { public void run() {
+            equal(startingGate.getPhase(), 0);
+            startingGate.arriveAndAwaitAdvance();
+            equal(startingGate.getPhase(), 1);
+            int phase = phaser.arrive();
+            if (phase == 0)
+                count0.getAndIncrement();
+            else if (phase == 1)
+                count1.getAndIncrement();
+            else
+                fail();
+        }};
+        for (int i = 0; i < nthreads; i++)
+            threads.add(new Thread(task));
+        for (Thread thread : threads)
+            thread.start();
+        for (Thread thread : threads)
+            thread.join();
+        equal(count0.get(), n);
+        equal(count1.get(), nthreads-n);
+        equal(phaser.getPhase(), 1);
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    volatile int passed = 0, failed = 0;
+    void pass() {passed++;}
+    void fail() {failed++; Thread.dumpStack();}
+    void fail(String msg) {System.err.println(msg); fail();}
+    void unexpected(Throwable t) {failed++; t.printStackTrace();}
+    void check(boolean cond) {if (cond) pass(); else fail();}
+    void equal(Object x, Object y) {
+        if (x == null ? y == null : x.equals(y)) pass();
+        else fail(x + " not equal to " + y);}
+    public static void main(String[] args) throws Throwable {
+        new Arrive().instanceMain(args);}
+    public void instanceMain(String[] args) throws Throwable {
+        try {test(args);} catch (Throwable t) {unexpected(t);}
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) throw new AssertionError("Some tests failed");}
+}

test/java/util/concurrent/Phaser/Basic.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+/*
+ * @test
+ * @bug 6445158
+ * @summary Basic tests for Phaser
+ * @author Chris Hegarty
+ */
+
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.concurrent.Phaser;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
+import static java.util.concurrent.TimeUnit.*;
+
+public class Basic {
+
+    private static void checkTerminated(final Phaser phaser) {
+        check(phaser.isTerminated());
+        int unarriverParties = phaser.getUnarrivedParties();
+        int registeredParties = phaser.getRegisteredParties();
+        equal(phaser.arrive(), -1);
+        equal(phaser.arriveAndDeregister(), -1);
+        equal(phaser.arriveAndAwaitAdvance(), -1);
+        equal(phaser.bulkRegister(10), -1);
+        equal(phaser.getPhase(), -1);
+        equal(phaser.register(), -1);
+        try {
+            equal(phaser.awaitAdvanceInterruptibly(0), -1);
+            equal(phaser.awaitAdvanceInterruptibly(0, 10, SECONDS), -1);
+        } catch (Exception ie) {
+            unexpected(ie);
+        }
+        equal(phaser.getUnarrivedParties(), unarriverParties);
+        equal(phaser.getRegisteredParties(), registeredParties);
+    }
+
+    private static void checkResult(Arriver a, Class<? extends Throwable> c) {
+        Throwable t = a.result();
+        if (! ((t == null && c == null) || (c != null && c.isInstance(t)))) {
+            //      t.printStackTrace();
+            fail("Mismatch in thread " +
+                 a.getName() + ": " +
+                 t + ", " +
+                 (c == null ? "<null>" : c.getName()));
+        } else {
+            pass();
+        }
+    }
+
+    //----------------------------------------------------------------
+    // Mechanism to get all test threads into "running" mode.
+    //----------------------------------------------------------------
+    private static Phaser atTheStartingGate = new Phaser(3);
+
+    private static void toTheStartingGate() {
+        try {
+            boolean expectNextPhase = false;
+            if (atTheStartingGate.getUnarrivedParties() == 1) {
+                expectNextPhase = true;
+            }
+            int phase = atTheStartingGate.getPhase();
+            equal(phase, atTheStartingGate.arrive());
+            int AwaitPhase = atTheStartingGate.awaitAdvanceInterruptibly(phase,
+                                                        10,
+                                                        SECONDS);
+            if (expectNextPhase) check(AwaitPhase == (phase + 1));
+
+            pass();
+        } catch (Throwable t) {
+            unexpected(t);
+           // reset(atTheStartingGate);
+            throw new Error(t);
+        }
+    }
+
+    //----------------------------------------------------------------
+    // Convenience methods for creating threads that call arrive,
+    // awaitAdvance, arriveAndAwaitAdvance, awaitAdvanceInterruptibly
+    //----------------------------------------------------------------
+    private static abstract class Arriver extends Thread {
+        static AtomicInteger count = new AtomicInteger(1);
+
+        Arriver() {
+            this("Arriver");
+        }
+
+        Arriver(String name) {
+            this.setName(name + ":" + count.getAndIncrement());
+            this.setDaemon(true);
+        }
+
+        private volatile Throwable result;
+        private volatile int phase;
+        protected void result(Throwable result) { this.result = result; }
+        public Throwable result() { return this.result; }
+        protected void phase(int phase) { this.phase = phase; }
+        public int phase() { return this.phase; }
+    }
+
+    private static abstract class Awaiter extends Arriver {
+        Awaiter() { super("Awaiter"); }
+        Awaiter(String name) { super(name); }
+    }
+
+    private static Arriver arriver(final Phaser phaser) {
+        return new Arriver() { public void run() {
+            toTheStartingGate();
+
+            try { phase(phaser.arrive()); }
+            catch (Throwable result) { result(result); }}};
+    }
+
+    private static AtomicInteger cycleArriveAwaitAdvance = new AtomicInteger(1);
+
+    private static Awaiter awaiter(final Phaser phaser) {
+        return new Awaiter() { public void run() {
+            toTheStartingGate();
+
+            try {
+                if (cycleArriveAwaitAdvance.getAndIncrement() % 2 == 0)
+                    phase(phaser.awaitAdvance(phaser.arrive()));
+                else
+                    phase(phaser.arriveAndAwaitAdvance());
+            } catch (Throwable result) { result(result); }}};
+    }
+
+    private static Awaiter awaiter(final Phaser phaser,
+                                   final long timeout,
+                                   final TimeUnit unit) {
+        return new Awaiter("InterruptibleWaiter") { public void run() {
+            toTheStartingGate();
+
+            try {
+                if (timeout < 0)
+                    phase(phaser.awaitAdvanceInterruptibly(phaser.arrive()));
+                else
+                    phase(phaser.awaitAdvanceInterruptibly(phaser.arrive(),
+                                                     timeout,
+                                                     unit));
+            } catch (Throwable result) { result(result); }}};
+    }
+
+    // Returns an infinite lazy list of all possible arriver/awaiter combinations.
+    private static Iterator<Arriver> arriverIterator(final Phaser phaser) {
+        return new Iterator<Arriver>() {
+            int i = 0;
+            public boolean hasNext() { return true; }
+            public Arriver next() {
+                switch ((i++)&7) {
+                    case 0: case 4:
+                        return arriver(phaser);
+                    case 1: case 5:
+                        return awaiter(phaser);
+                    case 2: case 6: case 7:
+                        return awaiter(phaser, -1, SECONDS);
+                    default:
+                        return awaiter(phaser, 10, SECONDS); }}
+            public void remove() {throw new UnsupportedOperationException();}};
+    }
+
+    // Returns an infinite lazy list of all possible awaiter only combinations.
+    private static Iterator<Awaiter> awaiterIterator(final Phaser phaser) {
+        return new Iterator<Awaiter>() {
+            int i = 0;
+            public boolean hasNext() { return true; }
+            public Awaiter next() {
+                switch ((i++)&7) {
+                    case 1: case 4: case 7:
+                        return awaiter(phaser);
+                    case 2: case 5:
+                        return awaiter(phaser, -1, SECONDS);
+                    default:
+                        return awaiter(phaser, 10, SECONDS); }}
+            public void remove() {throw new UnsupportedOperationException();}};
+    }
+
+    private static void realMain(String[] args) throws Throwable {
+
+        Thread.currentThread().setName("mainThread");
+
+        //----------------------------------------------------------------
+        // Normal use
+        //----------------------------------------------------------------
+        try {
+            Phaser phaser = new Phaser(3);
+            equal(phaser.getRegisteredParties(), 3);
+            equal(phaser.getArrivedParties(), 0);
+            equal(phaser.getPhase(), 0);
+            check(phaser.getRoot().equals(phaser));
+            equal(phaser.getParent(), null);
+            check(!phaser.isTerminated());
+
+            Iterator<Arriver> arrivers = arriverIterator(phaser);
+            int phase = 0;
+            for (int i = 0; i < 10; i++) {
+                equal(phaser.getPhase(), phase++);
+                Arriver a1 = arrivers.next(); a1.start();
+                Arriver a2 = arrivers.next(); a2.start();
+                toTheStartingGate();
+                phaser.arriveAndAwaitAdvance();
+                a1.join();
+                a2.join();
+                checkResult(a1, null);
+                checkResult(a2, null);
+                check(!phaser.isTerminated());
+                equal(phaser.getRegisteredParties(), 3);
+                equal(phaser.getArrivedParties(), 0);
+            }
+        } catch (Throwable t) { unexpected(t); }
+
+        //----------------------------------------------------------------
+        // One thread interrupted
+        //----------------------------------------------------------------
+        try {
+            Phaser phaser = new Phaser(3);
+            Iterator<Arriver> arrivers = arriverIterator(phaser);
+            int phase = phaser.getPhase();
+            for (int i = 0; i < 4; i++) {
+                check(phaser.getPhase() == phase);
+                Awaiter a1 = awaiter(phaser, 10, SECONDS); a1.start();
+                Arriver a2 = arrivers.next(); a2.start();
+                toTheStartingGate();
+                a1.interrupt();
+                a1.join();
+                phaser.arriveAndAwaitAdvance();
+                a2.join();
+                checkResult(a1, InterruptedException.class);
+                checkResult(a2, null);
+                check(!phaser.isTerminated());
+                equal(phaser.getRegisteredParties(), 3);
+                equal(phaser.getArrivedParties(), 0);
+                phase++;
+            }
+        } catch (Throwable t) { unexpected(t); }
+
+        //----------------------------------------------------------------
+        // Phaser is terminated while threads are waiting
+        //----------------------------------------------------------------
+        try {
+            Phaser phaser = new Phaser(3);
+            Iterator<Awaiter> awaiters = awaiterIterator(phaser);
+            for (int i = 0; i < 4; i++) {
+                Arriver a1 = awaiters.next(); a1.start();
+                Arriver a2 = awaiters.next(); a2.start();
+                toTheStartingGate();
+                while (phaser.getArrivedParties() < 2) Thread.yield();
+                phaser.forceTermination();
+                a1.join();
+                a2.join();
+                check(a1.phase == -1);
+                check(a2.phase == -1);
+                int arrivedParties = phaser.getArrivedParties();
+                checkTerminated(phaser);
+                equal(phaser.getArrivedParties(), arrivedParties);
+            }
+        } catch (Throwable t) { unexpected(t); }
+
+        //----------------------------------------------------------------
+        // Adds new unarrived parties to this phaser
+        //----------------------------------------------------------------
+        try {
+            Phaser phaser = new Phaser(1);
+            Iterator<Arriver> arrivers = arriverIterator(phaser);
+            LinkedList<Arriver> arriverList = new LinkedList<Arriver>();
+            int phase = phaser.getPhase();
+            for (int i = 1; i < 5; i++) {
+                atTheStartingGate = new Phaser(1+(3*i));
+                check(phaser.getPhase() == phase);
+                // register 3 more
+                phaser.register(); phaser.register(); phaser.register();
+                for (int z=0; z<(3*i); z++) {
+                   arriverList.add(arrivers.next());
+                }
+                for (Arriver arriver : arriverList)
+                    arriver.start();
+
+                toTheStartingGate();
+                phaser.arriveAndAwaitAdvance();
+
+                for (Arriver arriver : arriverList) {
+                    arriver.join();
+                    checkResult(arriver, null);
+                }
+                equal(phaser.getRegisteredParties(), 1 + (3*i));
+                equal(phaser.getArrivedParties(), 0);
+                arriverList.clear();
+                phase++;
+            }
+            atTheStartingGate = new Phaser(3);
+        } catch (Throwable t) { unexpected(t); }
+
+        //----------------------------------------------------------------
+        // One thread timed out
+        //----------------------------------------------------------------
+        try {
+            Phaser phaser = new Phaser(3);
+            Iterator<Arriver> arrivers = arriverIterator(phaser);
+            for (long timeout : new long[] { 0L, 5L }) {
+                for (int i = 0; i < 2; i++) {
+                    Awaiter a1 = awaiter(phaser, timeout, SECONDS); a1.start();
+                    Arriver a2 = arrivers.next();                   a2.start();
+                    toTheStartingGate();
+                    a1.join();
+                    checkResult(a1, TimeoutException.class);
+                    phaser.arrive();
+                    a2.join();
+                    checkResult(a2, null);
+                    check(!phaser.isTerminated());
+                }
+            }
+        } catch (Throwable t) { unexpected(t); }
+
+        //----------------------------------------------------------------
+        // Barrier action completed normally
+        //----------------------------------------------------------------
+        try {
+            final AtomicInteger count = new AtomicInteger(0);
+            final Phaser[] kludge = new Phaser[1];
+            Phaser phaser = new Phaser(3) {
+                @Override
+                protected boolean onAdvance(int phase, int registeredParties) {
+                    int countPhase = count.getAndIncrement();
+                    equal(countPhase, phase);
+                    equal(kludge[0].getPhase(), phase);
+                    equal(kludge[0].getRegisteredParties(), registeredParties);
+                    if (phase >= 3)
+                        return true; // terminate
+
+                    return false;
+                }
+            };
+            kludge[0] = phaser;
+            equal(phaser.getRegisteredParties(), 3);
+            Iterator<Awaiter> awaiters = awaiterIterator(phaser);
+            for (int i = 0; i < 4; i++) {
+                Awaiter a1 = awaiters.next(); a1.start();
+                Awaiter a2 = awaiters.next(); a2.start();
+                toTheStartingGate();
+                while (phaser.getArrivedParties() < 2) Thread.yield();
+                phaser.arrive();
+                a1.join();
+                a2.join();
+                checkResult(a1, null);
+                checkResult(a2, null);
+                equal(count.get(), i+1);
+                if (i < 3) {
+                    check(!phaser.isTerminated());
+                    equal(phaser.getRegisteredParties(), 3);
+                    equal(phaser.getArrivedParties(), 0);
+                    equal(phaser.getUnarrivedParties(), 3);
+                    equal(phaser.getPhase(), count.get());
+                } else
+                    checkTerminated(phaser);
+            }
+        } catch (Throwable t) { unexpected(t); }
+
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    static volatile int passed = 0, failed = 0;
+    static void pass() {passed++;}
+    static void fail() {failed++; Thread.dumpStack();}
+    static void fail(String msg) {System.out.println(msg); fail();}
+    static void unexpected(Throwable t) {failed++; t.printStackTrace();}
+    static void check(boolean cond) {if (cond) pass(); else fail();}
+    static void equal(Object x, Object y) {
+        if (x == null ? y == null : x.equals(y)) pass();
+        else fail(x + " not equal to " + y);}
+    public static void main(String[] args) throws Throwable {
+        try {realMain(args);} catch (Throwable t) {unexpected(t);}
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) throw new AssertionError("Some tests failed");}
+}

test/java/util/concurrent/ScheduledThreadPoolExecutor/DelayOverflow.java

@@ -20,6 +20,17 @@
  * have any questions.
  */
 
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
 /*
  * @test
  * @bug 6725789

test/java/util/concurrent/forkjoin/Integrate.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+/*
+ * @test
+ * @bug 6865571
+ * @summary Numerical Integration using fork/join
+ * @run main Integrate reps=1 forkPolicy=dynamic
+ * @run main Integrate reps=1 forkPolicy=serial
+ * @run main Integrate reps=1 forkPolicy=fork
+ */
+
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.RecursiveAction;
+
+/**
+ * Sample program using Gaussian Quadrature for numerical integration.
+ * This version uses a simplified hardwired function.  Inspired by a
+ * <A href="http://www.cs.uga.edu/~dkl/filaments/dist.html">
+ * Filaments</A> demo program.
+ */
+public final class Integrate {
+
+    static final double errorTolerance = 1.0e-11;
+    /** for time conversion */
+    static final long NPS = (1000L * 1000 * 1000);
+
+    static final int SERIAL = -1;
+    static final int DYNAMIC = 0;
+    static final int FORK = 1;
+
+    // the function to integrate
+    static double computeFunction(double x)  {
+        return (x * x + 1.0) * x;
+    }
+
+    static final double start = 0.0;
+    static final double end = 1536.0;
+    /*
+     * The number of recursive calls for
+     * integrate from start to end.
+     * (Empirically determined)
+     */
+    static final int calls = 263479047;
+
+    static String keywordValue(String[] args, String keyword) {
+        for (String arg : args)
+            if (arg.startsWith(keyword))
+                return arg.substring(keyword.length() + 1);
+        return null;
+    }
+
+    static int intArg(String[] args, String keyword, int defaultValue) {
+        String val = keywordValue(args, keyword);
+        return (val == null) ? defaultValue : Integer.parseInt(val);
+    }
+
+    static int policyArg(String[] args, String keyword, int defaultPolicy) {
+        String val = keywordValue(args, keyword);
+        if (val == null) return defaultPolicy;
+        if (val.equals("dynamic")) return DYNAMIC;
+        if (val.equals("serial")) return SERIAL;
+        if (val.equals("fork")) return FORK;
+        throw new Error();
+    }
+
+    /**
+     * Usage: Integrate [procs=N] [reps=N] forkPolicy=serial|dynamic|fork
+     */
+    public static void main(String[] args) throws Exception {
+        final int procs = intArg(args, "procs",
+                                 Runtime.getRuntime().availableProcessors());
+        final int forkPolicy = policyArg(args, "forkPolicy", DYNAMIC);
+
+        ForkJoinPool g = new ForkJoinPool(procs);
+        System.out.println("Integrating from " + start + " to " + end +
+                           " forkPolicy = " + forkPolicy);
+        long lastTime = System.nanoTime();
+
+        for (int reps = intArg(args, "reps", 10); reps > 0; reps--) {
+            double a;
+            if (forkPolicy == SERIAL)
+                a = SQuad.computeArea(g, start, end);
+            else if (forkPolicy == FORK)
+                a = FQuad.computeArea(g, start, end);
+            else
+                a = DQuad.computeArea(g, start, end);
+            long now = System.nanoTime();
+            double s = (double) (now - lastTime) / NPS;
+            lastTime = now;
+            System.out.printf("Calls/sec: %12d", (long) (calls / s));
+            System.out.printf(" Time: %7.3f", s);
+            System.out.printf(" Area: %12.1f", a);
+            System.out.println();
+        }
+        System.out.println(g);
+        g.shutdown();
+    }
+
+
+    // Sequential version
+    static final class SQuad extends RecursiveAction {
+        static double computeArea(ForkJoinPool pool, double l, double r) {
+            SQuad q = new SQuad(l, r, 0);
+            pool.invoke(q);
+            return q.area;
+        }
+
+        final double left;       // lower bound
+        final double right;      // upper bound
+        double area;
+
+        SQuad(double l, double r, double a) {
+            this.left = l; this.right = r; this.area = a;
+        }
+
+        public final void compute() {
+            double l = left;
+            double r = right;
+            area = recEval(l, r, (l * l + 1.0) * l, (r * r + 1.0) * r, area);
+        }
+
+        static final double recEval(double l, double r, double fl,
+                                    double fr, double a) {
+            double h = (r - l) * 0.5;
+            double c = l + h;
+            double fc = (c * c + 1.0) * c;
+            double hh = h * 0.5;
+            double al = (fl + fc) * hh;
+            double ar = (fr + fc) * hh;
+            double alr = al + ar;
+            if (Math.abs(alr - a) <= errorTolerance)
+                return alr;
+            else
+                return recEval(c, r, fc, fr, ar) + recEval(l, c, fl, fc, al);
+        }
+
+    }
+
+    //....................................
+
+    // ForkJoin version
+    static final class FQuad extends RecursiveAction {
+        static double computeArea(ForkJoinPool pool, double l, double r) {
+            FQuad q = new FQuad(l, r, 0);
+            pool.invoke(q);
+            return q.area;
+        }
+
+        final double left;       // lower bound
+        final double right;      // upper bound
+        double area;
+
+        FQuad(double l, double r, double a) {
+            this.left = l; this.right = r; this.area = a;
+        }
+
+        public final void compute() {
+            double l = left;
+            double r = right;
+            area = recEval(l, r, (l * l + 1.0) * l, (r * r + 1.0) * r, area);
+        }
+
+        static final double recEval(double l, double r, double fl,
+                                    double fr, double a) {
+            double h = (r - l) * 0.5;
+            double c = l + h;
+            double fc = (c * c + 1.0) * c;
+            double hh = h * 0.5;
+            double al = (fl + fc) * hh;
+            double ar = (fr + fc) * hh;
+            double alr = al + ar;
+            if (Math.abs(alr - a) <= errorTolerance)
+                return alr;
+            FQuad q = new FQuad(l, c, al);
+            q.fork();
+            ar = recEval(c, r, fc, fr, ar);
+            if (!q.tryUnfork()) {
+                q.quietlyHelpJoin();
+                return ar + q.area;
+            }
+            return ar + recEval(l, c, fl, fc, al);
+        }
+
+    }
+
+    // ...........................
+
+    // Version using on-demand Fork
+    static final class DQuad extends RecursiveAction {
+        static double computeArea(ForkJoinPool pool, double l, double r) {
+            DQuad q = new DQuad(l, r, 0);
+            pool.invoke(q);
+            return q.area;
+        }
+
+        final double left;       // lower bound
+        final double right;      // upper bound
+        double area;
+
+        DQuad(double l, double r, double a) {
+            this.left = l; this.right = r; this.area = a;
+        }
+
+        public final void compute() {
+            double l = left;
+            double r = right;
+            area = recEval(l, r, (l * l + 1.0) * l, (r * r + 1.0) * r, area);
+        }
+
+        static final double recEval(double l, double r, double fl,
+                                    double fr, double a) {
+            double h = (r - l) * 0.5;
+            double c = l + h;
+            double fc = (c * c + 1.0) * c;
+            double hh = h * 0.5;
+            double al = (fl + fc) * hh;
+            double ar = (fr + fc) * hh;
+            double alr = al + ar;
+            if (Math.abs(alr - a) <= errorTolerance)
+                return alr;
+            DQuad q = null;
+            if (getSurplusQueuedTaskCount() <= 3)
+                (q = new DQuad(l, c, al)).fork();
+            ar = recEval(c, r, fc, fr, ar);
+            if (q != null && !q.tryUnfork()) {
+                q.quietlyHelpJoin();
+                return ar + q.area;
+            }
+            return ar + recEval(l, c, fl, fc, al);
+        }
+
+    }
+
+}

test/java/util/concurrent/forkjoin/NQueensCS.java

+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/licenses/publicdomain
+ */
+
+/*
+ * @test
+ * @bug 6865571
+ * @summary Solve NQueens using fork/join
+ * @run main NQueensCS maxBoardSize=11 reps=1
+ * @run main NQueensCS maxBoardSize=11 reps=1 procs=8
+ */
+
+import java.util.Arrays;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.RecursiveAction;
+
+public class NQueensCS extends RecursiveAction {
+
+    static long lastStealCount;
+    static int boardSize;
+
+    static final int[] expectedSolutions = new int[] {
+        0, 1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2680, 14200,
+        73712, 365596, 2279184, 14772512, 95815104, 666090624
+    }; // see http://www.durangobill.com/N_Queens.html
+
+    static String keywordValue(String[] args, String keyword) {
+        for (String arg : args)
+            if (arg.startsWith(keyword))
+                return arg.substring(keyword.length() + 1);
+        return null;
+    }
+
+    static int intArg(String[] args, String keyword, int defaultValue) {
+        String val = keywordValue(args, keyword);
+        return (val == null) ? defaultValue : Integer.parseInt(val);
+    }
+
+    /** for time conversion */
+    static final long NPS = (1000L * 1000L * 1000L);
+
+    /**
+     * Usage: NQueensCS [minBoardSize=N] [maxBoardSize=N] [procs=N] [reps=N]
+     */
+    public static void main(String[] args) throws Exception {
+        // Board sizes too small: hard to measure well.
+        // Board sizes too large: take too long to run.
+        final int minBoardSize = intArg(args, "minBoardSize",  8);
+        final int maxBoardSize = intArg(args, "maxBoardSize", 15);
+
+        final int procs = intArg(args, "procs", 0);
+
+        for (int reps = intArg(args, "reps", 10); reps > 0; reps--) {
+            ForkJoinPool g = (procs == 0) ?
+                new ForkJoinPool() :
+                new ForkJoinPool(procs);
+            lastStealCount = g.getStealCount();
+            for (int i = minBoardSize; i <= maxBoardSize; i++)
+                test(g, i);
+            System.out.println(g);
+            g.shutdown();
+        }
+    }
+
+    static void test(ForkJoinPool g, int i) throws Exception {
+        boardSize = i;
+        int ps = g.getParallelism();
+        long start = System.nanoTime();
+        NQueensCS task = new NQueensCS(new int[0]);
+        g.invoke(task);
+        int solutions = task.solutions;
+        long time = System.nanoTime() - start;
+        double secs = (double) time / NPS;
+        if (solutions != expectedSolutions[i])
+            throw new Error();
+        System.out.printf("NQueensCS %3d", i);
+        System.out.printf(" Time: %7.3f", secs);
+        long sc = g.getStealCount();
+        long ns = sc - lastStealCount;
+        lastStealCount = sc;
+        System.out.printf(" Steals/t: %5d", ns/ps);
+        System.out.println();
+    }
+
+    // Boards are represented as arrays where each cell
+    // holds the column number of the queen in that row
+
+    final int[] sofar;
+    NQueensCS nextSubtask; // to link subtasks
+    int solutions;
+    NQueensCS(int[] a) {
+        this.sofar = a;
+    }
+
+    public final void compute() {
+        NQueensCS subtasks;
+        int bs = boardSize;
+        if (sofar.length >= bs)
+            solutions = 1;
+        else if ((subtasks = explore(sofar, bs)) != null)
+            solutions = processSubtasks(subtasks);
+    }
+
+    private static NQueensCS explore(int[] array, int bs) {
+        int row = array.length;
+        NQueensCS s = null; // subtask list
+        outer:
+        for (int q = 0; q < bs; ++q) {
+            for (int i = 0; i < row; i++) {
+                int p = array[i];
+                if (q == p || q == p - (row - i) || q == p + (row - i))
+                    continue outer; // attacked
+            }
+            NQueensCS first = s; // lag forks to ensure 1 kept
+            if (first != null)
+                first.fork();
+            int[] next = Arrays.copyOf(array, row+1);
+            next[row] = q;
+            NQueensCS subtask = new NQueensCS(next);
+            subtask.nextSubtask = first;
+            s = subtask;
+        }
+        return s;
+    }
+
+    private static int processSubtasks(NQueensCS s) {
+        // Always run first the task held instead of forked
+        s.compute();
+        int ns = s.solutions;
+        s = s.nextSubtask;
+        // Then the unstolen ones
+        while (s != null && s.tryUnfork()) {
+            s.compute();
+            ns += s.solutions;
+            s = s.nextSubtask;
+        }
+        // Then wait for the stolen ones
+        while (s != null) {
+            s.join();
+            ns += s.solutions;
+            s = s.nextSubtask;
+        }
+        return ns;
+    }
+}

test/java/util/concurrent/locks/ReentrantLock/CancelledLockLoops.java

@@ -115,7 +115,7 @@ public final class CancelledLockLoops {
             finally {
                 lock.unlock();
             }
-            if (completed != 2)
+            if (c != 2)
                 throw new Error("Completed != 2");
             int r = result;
             if (r == 0) // avoid overoptimization

test/java/util/concurrent/locks/ReentrantReadWriteLock/RWMap.java

@@ -30,6 +30,7 @@
  * Expert Group and released to the public domain, as explained at
  * http://creativecommons.org/licenses/publicdomain
  */
+
 import java.util.*;
 import java.util.concurrent.*;
 import java.util.concurrent.locks.*;