8019481: Sync misc j.u.c classes from 166 to tl

Reviewed-by: martin
Contributed-by: NDoug Lea <dl@cs.oswego.edu>

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

@@ -49,13 +49,13 @@ public class BrokenBarrierException extends Exception {
     private static final long serialVersionUID = 7117394618823254244L;
 
     /**
-     * Constructs a <tt>BrokenBarrierException</tt> with no specified detail
+     * Constructs a {@code BrokenBarrierException} with no specified detail
      * message.
      */
     public BrokenBarrierException() {}
 
     /**
-     * Constructs a <tt>BrokenBarrierException</tt> with the specified
+     * Constructs a {@code BrokenBarrierException} with the specified
      * detail message.
      *
      * @param message the detail message

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

@@ -92,15 +92,15 @@ import java.util.concurrent.locks.AbstractQueuedSynchronizer;
  *   private final CountDownLatch startSignal;
  *   private final CountDownLatch doneSignal;
  *   Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
- *      this.startSignal = startSignal;
- *      this.doneSignal = doneSignal;
+ *     this.startSignal = startSignal;
+ *     this.doneSignal = doneSignal;
  *   }
  *   public void run() {
- *      try {
- *        startSignal.await();
- *        doWork();
- *        doneSignal.countDown();
- *      } catch (InterruptedException ex) {} // return;
+ *     try {
+ *       startSignal.await();
+ *       doWork();
+ *       doneSignal.countDown();
+ *     } catch (InterruptedException ex) {} // return;
  *   }
  *
  *   void doWork() { ... }
@@ -130,14 +130,14 @@ import java.util.concurrent.locks.AbstractQueuedSynchronizer;
  *   private final CountDownLatch doneSignal;
  *   private final int i;
  *   WorkerRunnable(CountDownLatch doneSignal, int i) {
- *      this.doneSignal = doneSignal;
- *      this.i = i;
+ *     this.doneSignal = doneSignal;
+ *     this.i = i;
  *   }
  *   public void run() {
- *      try {
- *        doWork(i);
- *        doneSignal.countDown();
- *      } catch (InterruptedException ex) {} // return;
+ *     try {
+ *       doWork(i);
+ *       doneSignal.countDown();
+ *     } catch (InterruptedException ex) {} // return;
  *   }
  *
  *   void doWork() { ... }

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

@@ -45,14 +45,14 @@ import java.util.concurrent.locks.ReentrantLock;
  * <em>cyclic</em> because it can be re-used after the waiting threads
  * are released.
  *
- * <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
+ * <p>A {@code CyclicBarrier} supports an optional {@link Runnable} command
  * that is run once per barrier point, after the last thread in the party
  * arrives, but before any threads are released.
  * This <em>barrier action</em> is useful
  * for updating shared-state before any of the parties continue.
  *
- * <p><b>Sample usage:</b> Here is an example of
- *  using a barrier in a parallel decomposition design:
+ * <p><b>Sample usage:</b> Here is an example of using a barrier in a
+ * parallel decomposition design:
  *
  *  <pre> {@code
  * class Solver {
@@ -81,16 +81,20 @@ import java.util.concurrent.locks.ReentrantLock;
  *   public Solver(float[][] matrix) {
  *     data = matrix;
  *     N = matrix.length;
- *     barrier = new CyclicBarrier(N,
- *                                 new Runnable() {
- *                                   public void run() {
- *                                     mergeRows(...);
- *                                   }
- *                                 });
- *     for (int i = 0; i < N; ++i)
- *       new Thread(new Worker(i)).start();
+ *     Runnable barrierAction =
+ *       new Runnable() { public void run() { mergeRows(...); }};
+ *     barrier = new CyclicBarrier(N, barrierAction);
  *
- *     waitUntilDone();
+ *     List<Thread> threads = new ArrayList<Thread>(N);
+ *     for (int i = 0; i < N; i++) {
+ *       Thread thread = new Thread(new Worker(i));
+ *       threads.add(thread);
+ *       thread.start();
+ *     }
+ *
+ *     // wait until done
+ *     for (Thread thread : threads)
+ *       thread.join();
  *   }
  * }}</pre>
  *
@@ -98,8 +102,8 @@ import java.util.concurrent.locks.ReentrantLock;
  * barrier until all rows have been processed. When all rows are processed
  * the supplied {@link Runnable} barrier action is executed and merges the
  * rows. If the merger
- * determines that a solution has been found then <tt>done()</tt> will return
- * <tt>true</tt> and each worker will terminate.
+ * determines that a solution has been found then {@code done()} will return
+ * {@code true} and each worker will terminate.
  *
  * <p>If the barrier action does not rely on the parties being suspended when
  * it is executed, then any of the threads in the party could execute that
@@ -112,7 +116,7 @@ import java.util.concurrent.locks.ReentrantLock;
  *   // log the completion of this iteration
  * }}</pre>
  *
- * <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
+ * <p>The {@code CyclicBarrier} uses an all-or-none breakage model
  * for failed synchronization attempts: If a thread leaves a barrier
  * point prematurely because of interruption, failure, or timeout, all
  * other threads waiting at that barrier point will also leave
@@ -139,7 +143,7 @@ public class CyclicBarrier {
      * is reset. There can be many generations associated with threads
      * using the barrier - due to the non-deterministic way the lock
      * may be allocated to waiting threads - but only one of these
-     * can be active at a time (the one to which <tt>count</tt> applies)
+     * can be active at a time (the one to which {@code count} applies)
      * and all the rest are either broken or tripped.
      * There need not be an active generation if there has been a break
      * but no subsequent reset.
@@ -259,7 +263,7 @@ public class CyclicBarrier {
     }
 
     /**
-     * Creates a new <tt>CyclicBarrier</tt> that will trip when the
+     * Creates a new {@code CyclicBarrier} that will trip when the
      * given number of parties (threads) are waiting upon it, and which
      * will execute the given barrier action when the barrier is tripped,
      * performed by the last thread entering the barrier.
@@ -278,7 +282,7 @@ public class CyclicBarrier {
     }
 
     /**
-     * Creates a new <tt>CyclicBarrier</tt> that will trip when the
+     * Creates a new {@code CyclicBarrier} that will trip when the
      * given number of parties (threads) are waiting upon it, and
      * does not perform a predefined action when the barrier is tripped.
      *
@@ -301,7 +305,7 @@ public class CyclicBarrier {
 
     /**
      * Waits until all {@linkplain #getParties parties} have invoked
-     * <tt>await</tt> on this barrier.
+     * {@code await} on this barrier.
      *
      * <p>If the current thread is not the last to arrive then it is
      * disabled for thread scheduling purposes and lies dormant until
@@ -326,7 +330,7 @@ public class CyclicBarrier {
      *
      * <p>If the barrier is {@link #reset} while any thread is waiting,
      * or if the barrier {@linkplain #isBroken is broken} when
-     * <tt>await</tt> is invoked, or while any thread is waiting, then
+     * {@code await} is invoked, or while any thread is waiting, then
      * {@link BrokenBarrierException} is thrown.
      *
      * <p>If any thread is {@linkplain Thread#interrupt interrupted} while waiting,
@@ -343,7 +347,7 @@ public class CyclicBarrier {
      * the broken state.
      *
      * @return the arrival index of the current thread, where index
-     *         <tt>{@link #getParties()} - 1</tt> indicates the first
+     *         {@code getParties() - 1} indicates the first
      *         to arrive and zero indicates the last to arrive
      * @throws InterruptedException if the current thread was interrupted
      *         while waiting
@@ -351,7 +355,7 @@ public class CyclicBarrier {
      *         interrupted or timed out while the current thread was
      *         waiting, or the barrier was reset, or the barrier was
      *         broken when {@code await} was called, or the barrier
-     *         action (if present) failed due an exception.
+     *         action (if present) failed due to an exception
      */
     public int await() throws InterruptedException, BrokenBarrierException {
         try {
@@ -363,7 +367,7 @@ public class CyclicBarrier {
 
     /**
      * Waits until all {@linkplain #getParties parties} have invoked
-     * <tt>await</tt> on this barrier, or the specified waiting time elapses.
+     * {@code await} on this barrier, or the specified waiting time elapses.
      *
      * <p>If the current thread is not the last to arrive then it is
      * disabled for thread scheduling purposes and lies dormant until
@@ -393,7 +397,7 @@ public class CyclicBarrier {
      *
      * <p>If the barrier is {@link #reset} while any thread is waiting,
      * or if the barrier {@linkplain #isBroken is broken} when
-     * <tt>await</tt> is invoked, or while any thread is waiting, then
+     * {@code await} is invoked, or while any thread is waiting, then
      * {@link BrokenBarrierException} is thrown.
      *
      * <p>If any thread is {@linkplain Thread#interrupt interrupted} while
@@ -412,16 +416,17 @@ public class CyclicBarrier {
      * @param timeout the time to wait for the barrier
      * @param unit the time unit of the timeout parameter
      * @return the arrival index of the current thread, where index
-     *         <tt>{@link #getParties()} - 1</tt> indicates the first
+     *         {@code getParties() - 1} indicates the first
      *         to arrive and zero indicates the last to arrive
      * @throws InterruptedException if the current thread was interrupted
      *         while waiting
-     * @throws TimeoutException if the specified timeout elapses
+     * @throws TimeoutException if the specified timeout elapses.
+     *         In this case the barrier will be broken.
      * @throws BrokenBarrierException if <em>another</em> thread was
      *         interrupted or timed out while the current thread was
      *         waiting, or the barrier was reset, or the barrier was broken
      *         when {@code await} was called, or the barrier action (if
-     *         present) failed due an exception
+     *         present) failed due to an exception
      */
     public int await(long timeout, TimeUnit unit)
         throws InterruptedException,

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

@@ -35,7 +35,8 @@
  */
 
 package java.util.concurrent;
-import java.util.concurrent.atomic.*;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.LockSupport;
 
 /**
@@ -52,7 +53,7 @@ import java.util.concurrent.locks.LockSupport;
  * to swap buffers between threads so that the thread filling the
  * buffer gets a freshly emptied one when it needs it, handing off the
  * filled one to the thread emptying the buffer.
- * <pre>{@code
+ *  <pre> {@code
  * class FillAndEmpty {
  *   Exchanger<DataBuffer> exchanger = new Exchanger<DataBuffer>();
  *   DataBuffer initialEmptyBuffer = ... a made-up type
@@ -88,8 +89,7 @@ import java.util.concurrent.locks.LockSupport;
  *     new Thread(new FillingLoop()).start();
  *     new Thread(new EmptyingLoop()).start();
  *   }
- * }
- * }</pre>
+ * }}</pre>
  *
  * <p>Memory consistency effects: For each pair of threads that
  * successfully exchange objects via an {@code Exchanger}, actions
@@ -103,486 +103,425 @@ import java.util.concurrent.locks.LockSupport;
  * @param <V> The type of objects that may be exchanged
  */
 public class Exchanger<V> {
+
     /*
-     * Algorithm Description:
+     * Overview: The core algorithm is, for an exchange "slot",
+     * and a participant (caller) with an item:
+     *
+     * for (;;) {
+     *   if (slot is empty) {                       // offer
+     *     place item in a Node;
+     *     if (can CAS slot from empty to node) {
+     *       wait for release;
+     *       return matching item in node;
+     *     }
+     *   }
+     *   else if (can CAS slot from node to empty) { // release
+     *     get the item in node;
+     *     set matching item in node;
+     *     release waiting thread;
+     *   }
+     *   // else retry on CAS failure
+     * }
+     *
+     * This is among the simplest forms of a "dual data structure" --
+     * see Scott and Scherer's DISC 04 paper and
+     * http://www.cs.rochester.edu/research/synchronization/pseudocode/duals.html
      *
-     * The basic idea is to maintain a "slot", which is a reference to
-     * a Node containing both an Item to offer and a "hole" waiting to
-     * get filled in.  If an incoming "occupying" thread sees that the
-     * slot is null, it CAS'es (compareAndSets) a Node there and waits
-     * for another to invoke exchange.  That second "fulfilling" thread
-     * sees that the slot is non-null, and so CASes it back to null,
-     * also exchanging items by CASing the hole, plus waking up the
-     * occupying thread if it is blocked.  In each case CAS'es may
-     * fail because a slot at first appears non-null but is null upon
-     * CAS, or vice-versa.  So threads may need to retry these
-     * actions.
+     * This works great in principle. But in practice, like many
+     * algorithms centered on atomic updates to a single location, it
+     * scales horribly when there are more than a few participants
+     * using the same Exchanger. So the implementation instead uses a
+     * form of elimination arena, that spreads out this contention by
+     * arranging that some threads typically use different slots,
+     * while still ensuring that eventually, any two parties will be
+     * able to exchange items. That is, we cannot completely partition
+     * across threads, but instead give threads arena indices that
+     * will on average grow under contention and shrink under lack of
+     * contention. We approach this by defining the Nodes that we need
+     * anyway as ThreadLocals, and include in them per-thread index
+     * and related bookkeeping state. (We can safely reuse per-thread
+     * nodes rather than creating them fresh each time because slots
+     * alternate between pointing to a node vs null, so cannot
+     * encounter ABA problems. However, we do need some care in
+     * resetting them between uses.)
      *
-     * This simple approach works great when there are only a few
-     * threads using an Exchanger, but performance rapidly
-     * deteriorates due to CAS contention on the single slot when
-     * there are lots of threads using an exchanger.  So instead we use
-     * an "arena"; basically a kind of hash table with a dynamically
-     * varying number of slots, any one of which can be used by
-     * threads performing an exchange.  Incoming threads pick slots
-     * based on a hash of their Thread ids.  If an incoming thread
-     * fails to CAS in its chosen slot, it picks an alternative slot
-     * instead.  And similarly from there.  If a thread successfully
-     * CASes into a slot but no other thread arrives, it tries
-     * another, heading toward the zero slot, which always exists even
-     * if the table shrinks.  The particular mechanics controlling this
-     * are as follows:
+     * Implementing an effective arena requires allocating a bunch of
+     * space, so we only do so upon detecting contention (except on
+     * uniprocessors, where they wouldn't help, so aren't used).
+     * Otherwise, exchanges use the single-slot slotExchange method.
+     * On contention, not only must the slots be in different
+     * locations, but the locations must not encounter memory
+     * contention due to being on the same cache line (or more
+     * generally, the same coherence unit).  Because, as of this
+     * writing, there is no way to determine cacheline size, we define
+     * a value that is enough for common platforms.  Additionally,
+     * extra care elsewhere is taken to avoid other false/unintended
+     * sharing and to enhance locality, including adding padding (via
+     * sun.misc.Contended) to Nodes, embedding "bound" as an Exchanger
+     * field, and reworking some park/unpark mechanics compared to
+     * LockSupport versions.
      *
-     * Waiting: Slot zero is special in that it is the only slot that
-     * exists when there is no contention.  A thread occupying slot
-     * zero will block if no thread fulfills it after a short spin.
-     * In other cases, occupying threads eventually give up and try
-     * another slot.  Waiting threads spin for a while (a period that
-     * should be a little less than a typical context-switch time)
-     * before either blocking (if slot zero) or giving up (if other
-     * slots) and restarting.  There is no reason for threads to block
-     * unless there are unlikely to be any other threads present.
-     * Occupants are mainly avoiding memory contention so sit there
-     * quietly polling for a shorter period than it would take to
-     * block and then unblock them.  Non-slot-zero waits that elapse
-     * because of lack of other threads waste around one extra
-     * context-switch time per try, which is still on average much
-     * faster than alternative approaches.
+     * The arena starts out with only one used slot. We expand the
+     * effective arena size by tracking collisions; i.e., failed CASes
+     * while trying to exchange. By nature of the above algorithm, the
+     * only kinds of collision that reliably indicate contention are
+     * when two attempted releases collide -- one of two attempted
+     * offers can legitimately fail to CAS without indicating
+     * contention by more than one other thread. (Note: it is possible
+     * but not worthwhile to more precisely detect contention by
+     * reading slot values after CAS failures.)  When a thread has
+     * collided at each slot within the current arena bound, it tries
+     * to expand the arena size by one. We track collisions within
+     * bounds by using a version (sequence) number on the "bound"
+     * field, and conservatively reset collision counts when a
+     * participant notices that bound has been updated (in either
+     * direction).
      *
-     * Sizing: Usually, using only a few slots suffices to reduce
-     * contention.  Especially with small numbers of threads, using
-     * too many slots can lead to just as poor performance as using
-     * too few of them, and there's not much room for error.  The
-     * variable "max" maintains the number of slots actually in
-     * use.  It is increased when a thread sees too many CAS
-     * failures.  (This is analogous to resizing a regular hash table
-     * based on a target load factor, except here, growth steps are
-     * just one-by-one rather than proportional.)  Growth requires
-     * contention failures in each of three tried slots.  Requiring
-     * multiple failures for expansion copes with the fact that some
-     * failed CASes are not due to contention but instead to simple
-     * races between two threads or thread pre-emptions occurring
-     * between reading and CASing.  Also, very transient peak
-     * contention can be much higher than the average sustainable
-     * levels.  An attempt to decrease the max limit is usually made
-     * when a non-slot-zero wait elapses without being fulfilled.
-     * Threads experiencing elapsed waits move closer to zero, so
-     * eventually find existing (or future) threads even if the table
-     * has been shrunk due to inactivity.  The chosen mechanics and
-     * thresholds for growing and shrinking are intrinsically
-     * entangled with indexing and hashing inside the exchange code,
-     * and can't be nicely abstracted out.
+     * The effective arena size is reduced (when there is more than
+     * one slot) by giving up on waiting after a while and trying to
+     * decrement the arena size on expiration. The value of "a while"
+     * is an empirical matter.  We implement by piggybacking on the
+     * use of spin->yield->block that is essential for reasonable
+     * waiting performance anyway -- in a busy exchanger, offers are
+     * usually almost immediately released, in which case context
+     * switching on multiprocessors is extremely slow/wasteful.  Arena
+     * waits just omit the blocking part, and instead cancel. The spin
+     * count is empirically chosen to be a value that avoids blocking
+     * 99% of the time under maximum sustained exchange rates on a
+     * range of test machines. Spins and yields entail some limited
+     * randomness (using a cheap xorshift) to avoid regular patterns
+     * that can induce unproductive grow/shrink cycles. (Using a
+     * pseudorandom also helps regularize spin cycle duration by
+     * making branches unpredictable.)  Also, during an offer, a
+     * waiter can "know" that it will be released when its slot has
+     * changed, but cannot yet proceed until match is set.  In the
+     * mean time it cannot cancel the offer, so instead spins/yields.
+     * Note: It is possible to avoid this secondary check by changing
+     * the linearization point to be a CAS of the match field (as done
+     * in one case in the Scott & Scherer DISC paper), which also
+     * increases asynchrony a bit, at the expense of poorer collision
+     * detection and inability to always reuse per-thread nodes. So
+     * the current scheme is typically a better tradeoff.
      *
-     * Hashing: Each thread picks its initial slot to use in accord
-     * with a simple hashcode.  The sequence is the same on each
-     * encounter by any given thread, but effectively random across
-     * threads.  Using arenas encounters the classic cost vs quality
-     * tradeoffs of all hash tables.  Here, we use a one-step FNV-1a
-     * hash code based on the current thread's Thread.getId(), along
-     * with a cheap approximation to a mod operation to select an
-     * index.  The downside of optimizing index selection in this way
-     * is that the code is hardwired to use a maximum table size of
-     * 32.  But this value more than suffices for known platforms and
-     * applications.
+     * On collisions, indices traverse the arena cyclically in reverse
+     * order, restarting at the maximum index (which will tend to be
+     * sparsest) when bounds change. (On expirations, indices instead
+     * are halved until reaching 0.) It is possible (and has been
+     * tried) to use randomized, prime-value-stepped, or double-hash
+     * style traversal instead of simple cyclic traversal to reduce
+     * bunching.  But empirically, whatever benefits these may have
+     * don't overcome their added overhead: We are managing operations
+     * that occur very quickly unless there is sustained contention,
+     * so simpler/faster control policies work better than more
+     * accurate but slower ones.
      *
-     * Probing: On sensed contention of a selected slot, we probe
-     * sequentially through the table, analogously to linear probing
-     * after collision in a hash table.  (We move circularly, in
-     * reverse order, to mesh best with table growth and shrinkage
-     * rules.)  Except that to minimize the effects of false-alarms
-     * and cache thrashing, we try the first selected slot twice
-     * before moving.
+     * Because we use expiration for arena size control, we cannot
+     * throw TimeoutExceptions in the timed version of the public
+     * exchange method until the arena size has shrunken to zero (or
+     * the arena isn't enabled). This may delay response to timeout
+     * but is still within spec.
      *
-     * Padding: Even with contention management, slots are heavily
-     * contended, so use cache-padding to avoid poor memory
-     * performance.  Because of this, slots are lazily constructed
-     * only when used, to avoid wasting this space unnecessarily.
-     * While isolation of locations is not much of an issue at first
-     * in an application, as time goes on and garbage-collectors
-     * perform compaction, slots are very likely to be moved adjacent
-     * to each other, which can cause much thrashing of cache lines on
-     * MPs unless padding is employed.
+     * Essentially all of the implementation is in methods
+     * slotExchange and arenaExchange. These have similar overall
+     * structure, but differ in too many details to combine. The
+     * slotExchange method uses the single Exchanger field "slot"
+     * rather than arena array elements. However, it still needs
+     * minimal collision detection to trigger arena construction.
+     * (The messiest part is making sure interrupt status and
+     * InterruptedExceptions come out right during transitions when
+     * both methods may be called. This is done by using null return
+     * as a sentinel to recheck interrupt status.)
      *
-     * This is an improvement of the algorithm described in the paper
-     * "A Scalable Elimination-based Exchange Channel" by William
-     * Scherer, Doug Lea, and Michael Scott in Proceedings of SCOOL05
-     * workshop.  Available at: http://hdl.handle.net/1802/2104
+     * As is too common in this sort of code, methods are monolithic
+     * because most of the logic relies on reads of fields that are
+     * maintained as local variables so can't be nicely factored --
+     * mainly, here, bulky spin->yield->block/cancel code), and
+     * heavily dependent on intrinsics (Unsafe) to use inlined
+     * embedded CAS and related memory access operations (that tend
+     * not to be as readily inlined by dynamic compilers when they are
+     * hidden behind other methods that would more nicely name and
+     * encapsulate the intended effects). This includes the use of
+     * putOrderedX to clear fields of the per-thread Nodes between
+     * uses. Note that field Node.item is not declared as volatile
+     * even though it is read by releasing threads, because they only
+     * do so after CAS operations that must precede access, and all
+     * uses by the owning thread are otherwise acceptably ordered by
+     * other operations. (Because the actual points of atomicity are
+     * slot CASes, it would also be legal for the write to Node.match
+     * in a release to be weaker than a full volatile write. However,
+     * this is not done because it could allow further postponement of
+     * the write, delaying progress.)
      */
 
-    /** The number of CPUs, for sizing and spin control */
-    private static final int NCPU = Runtime.getRuntime().availableProcessors();
-
     /**
-     * The capacity of the arena.  Set to a value that provides more
-     * than enough space to handle contention.  On small machines
-     * most slots won't be used, but it is still not wasted because
-     * the extra space provides some machine-level address padding
-     * to minimize interference with heavily CAS'ed Slot locations.
-     * And on very large machines, performance eventually becomes
-     * bounded by memory bandwidth, not numbers of threads/CPUs.
-     * This constant cannot be changed without also modifying
-     * indexing and hashing algorithms.
+     * The byte distance (as a shift value) between any two used slots
+     * in the arena.  1 << ASHIFT should be at least cacheline size.
      */
-    private static final int CAPACITY = 32;
+    private static final int ASHIFT = 7;
 
     /**
-     * The value of "max" that will hold all threads without
-     * contention.  When this value is less than CAPACITY, some
-     * otherwise wasted expansion can be avoided.
+     * The maximum supported arena index. The maximum allocatable
+     * arena size is MMASK + 1. Must be a power of two minus one, less
+     * than (1<<(31-ASHIFT)). The cap of 255 (0xff) more than suffices
+     * for the expected scaling limits of the main algorithms.
      */
-    private static final int FULL =
-        Math.max(0, Math.min(CAPACITY, NCPU / 2) - 1);
+    private static final int MMASK = 0xff;
 
     /**
-     * The number of times to spin (doing nothing except polling a
-     * memory location) before blocking or giving up while waiting to
-     * be fulfilled.  Should be zero on uniprocessors.  On
-     * multiprocessors, this value should be large enough so that two
-     * threads exchanging items as fast as possible block only when
-     * one of them is stalled (due to GC or preemption), but not much
-     * longer, to avoid wasting CPU resources.  Seen differently, this
-     * value is a little over half the number of cycles of an average
-     * context switch time on most systems.  The value here is
-     * approximately the average of those across a range of tested
-     * systems.
+     * Unit for sequence/version bits of bound field. Each successful
+     * change to the bound also adds SEQ.
      */
-    private static final int SPINS = (NCPU == 1) ? 0 : 2000;
+    private static final int SEQ = MMASK + 1;
+
+    /** The number of CPUs, for sizing and spin control */
+    private static final int NCPU = Runtime.getRuntime().availableProcessors();
 
     /**
-     * The number of times to spin before blocking in timed waits.
-     * Timed waits spin more slowly because checking the time takes
-     * time.  The best value relies mainly on the relative rate of
-     * System.nanoTime vs memory accesses.  The value is empirically
-     * derived to work well across a variety of systems.
+     * The maximum slot index of the arena: The number of slots that
+     * can in principle hold all threads without contention, or at
+     * most the maximum indexable value.
      */
-    private static final int TIMED_SPINS = SPINS / 20;
+    static final int FULL = (NCPU >= (MMASK << 1)) ? MMASK : NCPU >>> 1;
 
     /**
-     * Sentinel item representing cancellation of a wait due to
-     * interruption, timeout, or elapsed spin-waits.  This value is
-     * placed in holes on cancellation, and used as a return value
-     * from waiting methods to indicate failure to set or get hole.
+     * The bound for spins while waiting for a match. The actual
+     * number of iterations will on average be about twice this value
+     * due to randomization. Note: Spinning is disabled when NCPU==1.
      */
-    private static final Object CANCEL = new Object();
+    private static final int SPINS = 1 << 10;
 
     /**
      * Value representing null arguments/returns from public
-     * methods.  This disambiguates from internal requirement that
-     * holes start out as null to mean they are not yet set.
+     * methods. Needed because the API originally didn't disallow null
+     * arguments, which it should have.
      */
     private static final Object NULL_ITEM = new Object();
 
     /**
-     * Nodes hold partially exchanged data.  This class
-     * opportunistically subclasses AtomicReference to represent the
-     * hole.  So get() returns hole, and compareAndSet CAS'es value
-     * into hole.  This class cannot be parameterized as "V" because
-     * of the use of non-V CANCEL sentinels.
+     * Sentinel value returned by internal exchange methods upon
+     * timeout, to avoid need for separate timed versions of these
+     * methods.
      */
-    @SuppressWarnings("serial")
-    private static final class Node extends AtomicReference<Object> {
-        /** The element offered by the Thread creating this node. */
-        public final Object item;
-
-        /** The Thread waiting to be signalled; null until waiting. */
-        public volatile Thread waiter;
-
-        /**
-         * Creates node with given item and empty hole.
-         * @param item the item
-         */
-        public Node(Object item) {
-            this.item = item;
-        }
-    }
+    private static final Object TIMED_OUT = new Object();
 
     /**
-     * A Slot is an AtomicReference with heuristic padding to lessen
-     * cache effects of this heavily CAS'ed location.  While the
-     * padding adds noticeable space, all slots are created only on
-     * demand, and there will be more than one of them only when it
-     * would improve throughput more than enough to outweigh using
-     * extra space.
+     * Nodes hold partially exchanged data, plus other per-thread
+     * bookkeeping. Padded via @sun.misc.Contended to reduce memory
+     * contention.
      */
-    @SuppressWarnings("serial")
-    private static final class Slot extends AtomicReference<Object> {
-        // Improve likelihood of isolation on <= 64 byte cache lines
-        long q0, q1, q2, q3, q4, q5, q6, q7, q8, q9, qa, qb, qc, qd, qe;
+    @sun.misc.Contended static final class Node {
+        int index;              // Arena index
+        int bound;              // Last recorded value of Exchanger.bound
+        int collides;           // Number of CAS failures at current bound
+        int hash;               // Pseudo-random for spins
+        Object item;            // This thread's current item
+        volatile Object match;  // Item provided by releasing thread
+        volatile Thread parked; // Set to this thread when parked, else null
     }
 
-    /**
-     * Slot array.  Elements are lazily initialized when needed.
-     * Declared volatile to enable double-checked lazy construction.
-     */
-    private volatile Slot[] arena = new Slot[CAPACITY];
-
-    /**
-     * The maximum slot index being used.  The value sometimes
-     * increases when a thread experiences too many CAS contentions,
-     * and sometimes decreases when a spin-wait elapses.  Changes
-     * are performed only via compareAndSet, to avoid stale values
-     * when a thread happens to stall right before setting.
-     */
-    private final AtomicInteger max = new AtomicInteger();
-
-    /**
-     * Main exchange function, handling the different policy variants.
-     * Uses Object, not "V" as argument and return value to simplify
-     * handling of sentinel values.  Callers from public methods decode
-     * and cast accordingly.
-     *
-     * @param item the (non-null) item to exchange
-     * @param timed true if the wait is timed
-     * @param nanos if timed, the maximum wait time
-     * @return the other thread's item, or CANCEL if interrupted or timed out
-     */
-    private Object doExchange(Object item, boolean timed, long nanos) {
-        Node me = new Node(item);                 // Create in case occupying
-        int index = hashIndex();                  // Index of current slot
-        int fails = 0;                            // Number of CAS failures
-
-        for (;;) {
-            Object y;                             // Contents of current slot
-            Slot slot = arena[index];
-            if (slot == null)                     // Lazily initialize slots
-                createSlot(index);                // Continue loop to reread
-            else if ((y = slot.get()) != null &&  // Try to fulfill
-                     slot.compareAndSet(y, null)) {
-                Node you = (Node)y;               // Transfer item
-                if (you.compareAndSet(null, item)) {
-                    LockSupport.unpark(you.waiter);
-                    return you.item;
-                }                                 // Else cancelled; continue
-            }
-            else if (y == null &&                 // Try to occupy
-                     slot.compareAndSet(null, me)) {
-                if (index == 0)                   // Blocking wait for slot 0
-                    return timed ?
-                        awaitNanos(me, slot, nanos) :
-                        await(me, slot);
-                Object v = spinWait(me, slot);    // Spin wait for non-0
-                if (v != CANCEL)
-                    return v;
-                me = new Node(item);              // Throw away cancelled node
-                int m = max.get();
-                if (m > (index >>>= 1))           // Decrease index
-                    max.compareAndSet(m, m - 1);  // Maybe shrink table
-            }
-            else if (++fails > 1) {               // Allow 2 fails on 1st slot
-                int m = max.get();
-                if (fails > 3 && m < FULL && max.compareAndSet(m, m + 1))
-                    index = m + 1;                // Grow on 3rd failed slot
-                else if (--index < 0)
-                    index = m;                    // Circularly traverse
-            }
-        }
-    }
-
-    /**
-     * Returns a hash index for the current thread.  Uses a one-step
-     * FNV-1a hash code (http://www.isthe.com/chongo/tech/comp/fnv/)
-     * based on the current thread's Thread.getId().  These hash codes
-     * have more uniform distribution properties with respect to small
-     * moduli (here 1-31) than do other simple hashing functions.
-     *
-     * <p>To return an index between 0 and max, we use a cheap
-     * approximation to a mod operation, that also corrects for bias
-     * due to non-power-of-2 remaindering (see {@link
-     * java.util.Random#nextInt}).  Bits of the hashcode are masked
-     * with "nbits", the ceiling power of two of table size (looked up
-     * in a table packed into three ints).  If too large, this is
-     * retried after rotating the hash by nbits bits, while forcing new
-     * top bit to 0, which guarantees eventual termination (although
-     * with a non-random-bias).  This requires an average of less than
-     * 2 tries for all table sizes, and has a maximum 2% difference
-     * from perfectly uniform slot probabilities when applied to all
-     * possible hash codes for sizes less than 32.
-     *
-     * @return a per-thread-random index, 0 <= index < max
-     */
-    private final int hashIndex() {
-        long id = Thread.currentThread().getId();
-        int hash = (((int)(id ^ (id >>> 32))) ^ 0x811c9dc5) * 0x01000193;
-
-        int m = max.get();
-        int nbits = (((0xfffffc00  >> m) & 4) | // Compute ceil(log2(m+1))
-                     ((0x000001f8 >>> m) & 2) | // The constants hold
-                     ((0xffff00f2 >>> m) & 1)); // a lookup table
-        int index;
-        while ((index = hash & ((1 << nbits) - 1)) > m)       // May retry on
-            hash = (hash >>> nbits) | (hash << (33 - nbits)); // non-power-2 m
-        return index;
+    /** The corresponding thread local class */
+    static final class Participant extends ThreadLocal<Node> {
+        public Node initialValue() { return new Node(); }
     }
 
     /**
-     * Creates a new slot at given index.  Called only when the slot
-     * appears to be null.  Relies on double-check using builtin
-     * locks, since they rarely contend.  This in turn relies on the
-     * arena array being declared volatile.
-     *
-     * @param index the index to add slot at
+     * Per-thread state
      */
-    private void createSlot(int index) {
-        // Create slot outside of lock to narrow sync region
-        Slot newSlot = new Slot();
-        Slot[] a = arena;
-        synchronized (a) {
-            if (a[index] == null)
-                a[index] = newSlot;
-        }
-    }
+    private final Participant participant;
 
     /**
-     * Tries to cancel a wait for the given node waiting in the given
-     * slot, if so, helping clear the node from its slot to avoid
-     * garbage retention.
-     *
-     * @param node the waiting node
-     * @param the slot it is waiting in
-     * @return true if successfully cancelled
+     * Elimination array; null until enabled (within slotExchange).
+     * Element accesses use emulation of volatile gets and CAS.
      */
-    private static boolean tryCancel(Node node, Slot slot) {
-        if (!node.compareAndSet(null, CANCEL))
-            return false;
-        if (slot.get() == node) // pre-check to minimize contention
-            slot.compareAndSet(node, null);
-        return true;
-    }
-
-    // Three forms of waiting. Each just different enough not to merge
-    // code with others.
+    private volatile Node[] arena;
 
     /**
-     * Spin-waits for hole for a non-0 slot.  Fails if spin elapses
-     * before hole filled.  Does not check interrupt, relying on check
-     * in public exchange method to abort if interrupted on entry.
-     *
-     * @param node the waiting node
-     * @return on success, the hole; on failure, CANCEL
+     * Slot used until contention detected.
      */
-    private static Object spinWait(Node node, Slot slot) {
-        int spins = SPINS;
-        for (;;) {
-            Object v = node.get();
-            if (v != null)
-                return v;
-            else if (spins > 0)
-                --spins;
-            else
-                tryCancel(node, slot);
-        }
-    }
+    private volatile Node slot;
 
     /**
-     * Waits for (by spinning and/or blocking) and gets the hole
-     * filled in by another thread.  Fails if interrupted before
-     * hole filled.
-     *
-     * When a node/thread is about to block, it sets its waiter field
-     * and then rechecks state at least one more time before actually
-     * parking, thus covering race vs fulfiller noticing that waiter
-     * is non-null so should be woken.
-     *
-     * Thread interruption status is checked only surrounding calls to
-     * park.  The caller is assumed to have checked interrupt status
-     * on entry.
-     *
-     * @param node the waiting node
-     * @return on success, the hole; on failure, CANCEL
+     * The index of the largest valid arena position, OR'ed with SEQ
+     * number in high bits, incremented on each update.  The initial
+     * update from 0 to SEQ is used to ensure that the arena array is
+     * constructed only once.
      */
-    private static Object await(Node node, Slot slot) {
-        Thread w = Thread.currentThread();
-        int spins = SPINS;
-        for (;;) {
-            Object v = node.get();
-            if (v != null)
-                return v;
-            else if (spins > 0)                 // Spin-wait phase
-                --spins;
-            else if (node.waiter == null)       // Set up to block next
-                node.waiter = w;
-            else if (w.isInterrupted())         // Abort on interrupt
-                tryCancel(node, slot);
-            else                                // Block
-                LockSupport.park(node);
-        }
-    }
+    private volatile int bound;
 
     /**
-     * Waits for (at index 0) and gets the hole filled in by another
-     * thread.  Fails if timed out or interrupted before hole filled.
-     * Same basic logic as untimed version, but a bit messier.
+     * Exchange function when arenas enabled. See above for explanation.
      *
-     * @param node the waiting node
-     * @param nanos the wait time
-     * @return on success, the hole; on failure, CANCEL
+     * @param item the (non-null) item to exchange
+     * @param timed true if the wait is timed
+     * @param ns if timed, the maximum wait time, else 0L
+     * @return the other thread's item; or null if interrupted; or
+     * TIMED_OUT if timed and timed out
      */
-    private Object awaitNanos(Node node, Slot slot, long nanos) {
-        int spins = TIMED_SPINS;
-        long lastTime = 0;
-        Thread w = null;
-        for (;;) {
-            Object v = node.get();
-            if (v != null)
+    private final Object arenaExchange(Object item, boolean timed, long ns) {
+        Node[] a = arena;
+        Node p = participant.get();
+        for (int i = p.index;;) {                      // access slot at i
+            int b, m, c; long j;                       // j is raw array offset
+            Node q = (Node)U.getObjectVolatile(a, j = (i << ASHIFT) + ABASE);
+            if (q != null && U.compareAndSwapObject(a, j, q, null)) {
+                Object v = q.item;                     // release
+                q.match = item;
+                Thread w = q.parked;
+                if (w != null)
+                    U.unpark(w);
                 return v;
-            long now = System.nanoTime();
-            if (w == null)
-                w = Thread.currentThread();
-            else
-                nanos -= now - lastTime;
-            lastTime = now;
-            if (nanos > 0) {
-                if (spins > 0)
-                    --spins;
-                else if (node.waiter == null)
-                    node.waiter = w;
-                else if (w.isInterrupted())
-                    tryCancel(node, slot);
+            }
+            else if (i <= (m = (b = bound) & MMASK) && q == null) {
+                p.item = item;                         // offer
+                if (U.compareAndSwapObject(a, j, null, p)) {
+                    long end = (timed && m == 0) ? System.nanoTime() + ns : 0L;
+                    Thread t = Thread.currentThread(); // wait
+                    for (int h = p.hash, spins = SPINS;;) {
+                        Object v = p.match;
+                        if (v != null) {
+                            U.putOrderedObject(p, MATCH, null);
+                            p.item = null;             // clear for next use
+                            p.hash = h;
+                            return v;
+                        }
+                        else if (spins > 0) {
+                            h ^= h << 1; h ^= h >>> 3; h ^= h << 10; // xorshift
+                            if (h == 0)                // initialize hash
+                                h = SPINS | (int)t.getId();
+                            else if (h < 0 &&          // approx 50% true
+                                     (--spins & ((SPINS >>> 1) - 1)) == 0)
+                                Thread.yield();        // two yields per wait
+                        }
+                        else if (U.getObjectVolatile(a, j) != p)
+                            spins = SPINS;       // releaser hasn't set match yet
+                        else if (!t.isInterrupted() && m == 0 &&
+                                 (!timed ||
+                                  (ns = end - System.nanoTime()) > 0L)) {
+                            U.putObject(t, BLOCKER, this); // emulate LockSupport
+                            p.parked = t;              // minimize window
+                            if (U.getObjectVolatile(a, j) == p)
+                                U.park(false, ns);
+                            p.parked = null;
+                            U.putObject(t, BLOCKER, null);
+                        }
+                        else if (U.getObjectVolatile(a, j) == p &&
+                                 U.compareAndSwapObject(a, j, p, null)) {
+                            if (m != 0)                // try to shrink
+                                U.compareAndSwapInt(this, BOUND, b, b + SEQ - 1);
+                            p.item = null;
+                            p.hash = h;
+                            i = p.index >>>= 1;        // descend
+                            if (Thread.interrupted())
+                                return null;
+                            if (timed && m == 0 && ns <= 0L)
+                                return TIMED_OUT;
+                            break;                     // expired; restart
+                        }
+                    }
+                }
                 else
-                    LockSupport.parkNanos(node, nanos);
+                    p.item = null;                     // clear offer
+            }
+            else {
+                if (p.bound != b) {                    // stale; reset
+                    p.bound = b;
+                    p.collides = 0;
+                    i = (i != m || m == 0) ? m : m - 1;
+                }
+                else if ((c = p.collides) < m || m == FULL ||
+                         !U.compareAndSwapInt(this, BOUND, b, b + SEQ + 1)) {
+                    p.collides = c + 1;
+                    i = (i == 0) ? m : i - 1;          // cyclically traverse
+                }
+                else
+                    i = m + 1;                         // grow
+                p.index = i;
             }
-            else if (tryCancel(node, slot) && !w.isInterrupted())
-                return scanOnTimeout(node);
         }
     }
 
     /**
-     * Sweeps through arena checking for any waiting threads.  Called
-     * only upon return from timeout while waiting in slot 0.  When a
-     * thread gives up on a timed wait, it is possible that a
-     * previously-entered thread is still waiting in some other
-     * slot.  So we scan to check for any.  This is almost always
-     * overkill, but decreases the likelihood of timeouts when there
-     * are other threads present to far less than that in lock-based
-     * exchangers in which earlier-arriving threads may still be
-     * waiting on entry locks.
+     * Exchange function used until arenas enabled. See above for explanation.
      *
-     * @param node the waiting node
-     * @return another thread's item, or CANCEL
+     * @param item the item to exchange
+     * @param timed true if the wait is timed
+     * @param ns if timed, the maximum wait time, else 0L
+     * @return the other thread's item; or null if either the arena
+     * was enabled or the thread was interrupted before completion; or
+     * TIMED_OUT if timed and timed out
      */
-    private Object scanOnTimeout(Node node) {
-        Object y;
-        for (int j = arena.length - 1; j >= 0; --j) {
-            Slot slot = arena[j];
-            if (slot != null) {
-                while ((y = slot.get()) != null) {
-                    if (slot.compareAndSet(y, null)) {
-                        Node you = (Node)y;
-                        if (you.compareAndSet(null, node.item)) {
-                            LockSupport.unpark(you.waiter);
-                            return you.item;
-                        }
-                    }
+    private final Object slotExchange(Object item, boolean timed, long ns) {
+        Node p = participant.get();
+        Thread t = Thread.currentThread();
+        if (t.isInterrupted()) // preserve interrupt status so caller can recheck
+            return null;
+
+        for (Node q;;) {
+            if ((q = slot) != null) {
+                if (U.compareAndSwapObject(this, SLOT, q, null)) {
+                    Object v = q.item;
+                    q.match = item;
+                    Thread w = q.parked;
+                    if (w != null)
+                        U.unpark(w);
+                    return v;
                 }
+                // create arena on contention, but continue until slot null
+                if (NCPU > 1 && bound == 0 &&
+                    U.compareAndSwapInt(this, BOUND, 0, SEQ))
+                    arena = new Node[(FULL + 2) << ASHIFT];
+            }
+            else if (arena != null)
+                return null; // caller must reroute to arenaExchange
+            else {
+                p.item = item;
+                if (U.compareAndSwapObject(this, SLOT, null, p))
+                    break;
+                p.item = null;
             }
         }
-        return CANCEL;
+
+        // await release
+        int h = p.hash;
+        long end = timed ? System.nanoTime() + ns : 0L;
+        int spins = (NCPU > 1) ? SPINS : 1;
+        Object v;
+        while ((v = p.match) == null) {
+            if (spins > 0) {
+                h ^= h << 1; h ^= h >>> 3; h ^= h << 10;
+                if (h == 0)
+                    h = SPINS | (int)t.getId();
+                else if (h < 0 && (--spins & ((SPINS >>> 1) - 1)) == 0)
+                    Thread.yield();
+            }
+            else if (slot != p)
+                spins = SPINS;
+            else if (!t.isInterrupted() && arena == null &&
+                     (!timed || (ns = end - System.nanoTime()) > 0L)) {
+                U.putObject(t, BLOCKER, this);
+                p.parked = t;
+                if (slot == p)
+                    U.park(false, ns);
+                p.parked = null;
+                U.putObject(t, BLOCKER, null);
+            }
+            else if (U.compareAndSwapObject(this, SLOT, p, null)) {
+                v = timed && ns <= 0L && !t.isInterrupted() ? TIMED_OUT : null;
+                break;
+            }
+        }
+        U.putOrderedObject(p, MATCH, null);
+        p.item = null;
+        p.hash = h;
+        return v;
     }
 
     /**
      * Creates a new Exchanger.
      */
     public Exchanger() {
+        participant = new Participant();
     }
 
     /**
@@ -620,15 +559,14 @@ public class Exchanger<V> {
      */
     @SuppressWarnings("unchecked")
     public V exchange(V x) throws InterruptedException {
-        if (!Thread.interrupted()) {
-            Object o = doExchange((x == null) ? NULL_ITEM : x, false, 0);
-            if (o == NULL_ITEM)
-                return null;
-            if (o != CANCEL)
-                return (V)o;
-            Thread.interrupted(); // Clear interrupt status on IE throw
-        }
-        throw new InterruptedException();
+        Object v;
+        Object item = (x == null) ? NULL_ITEM : x; // translate null args
+        if ((arena != null ||
+             (v = slotExchange(item, false, 0L)) == null) &&
+            ((Thread.interrupted() || // disambiguates null return
+              (v = arenaExchange(item, false, 0L)) == null)))
+            throw new InterruptedException();
+        return (v == NULL_ITEM) ? null : (V)v;
     }
 
     /**
@@ -666,7 +604,7 @@ public class Exchanger<V> {
      *
      * @param x the object to exchange
      * @param timeout the maximum time to wait
-     * @param unit the time unit of the <tt>timeout</tt> argument
+     * @param unit the time unit of the {@code timeout} argument
      * @return the object provided by the other thread
      * @throws InterruptedException if the current thread was
      *         interrupted while waiting
@@ -676,16 +614,51 @@ public class Exchanger<V> {
     @SuppressWarnings("unchecked")
     public V exchange(V x, long timeout, TimeUnit unit)
         throws InterruptedException, TimeoutException {
-        if (!Thread.interrupted()) {
-            Object o = doExchange((x == null) ? NULL_ITEM : x,
-                                  true, unit.toNanos(timeout));
-            if (o == NULL_ITEM)
-                return null;
-            if (o != CANCEL)
-                return (V)o;
-            if (!Thread.interrupted())
-                throw new TimeoutException();
+        Object v;
+        Object item = (x == null) ? NULL_ITEM : x;
+        long ns = unit.toNanos(timeout);
+        if ((arena != null ||
+             (v = slotExchange(item, true, ns)) == null) &&
+            ((Thread.interrupted() ||
+              (v = arenaExchange(item, true, ns)) == null)))
+            throw new InterruptedException();
+        if (v == TIMED_OUT)
+            throw new TimeoutException();
+        return (v == NULL_ITEM) ? null : (V)v;
+    }
+
+    // Unsafe mechanics
+    private static final sun.misc.Unsafe U;
+    private static final long BOUND;
+    private static final long SLOT;
+    private static final long MATCH;
+    private static final long BLOCKER;
+    private static final int ABASE;
+    static {
+        int s;
+        try {
+            U = sun.misc.Unsafe.getUnsafe();
+            Class<?> ek = Exchanger.class;
+            Class<?> nk = Node.class;
+            Class<?> ak = Node[].class;
+            Class<?> tk = Thread.class;
+            BOUND = U.objectFieldOffset
+                (ek.getDeclaredField("bound"));
+            SLOT = U.objectFieldOffset
+                (ek.getDeclaredField("slot"));
+            MATCH = U.objectFieldOffset
+                (nk.getDeclaredField("match"));
+            BLOCKER = U.objectFieldOffset
+                (tk.getDeclaredField("parkBlocker"));
+            s = U.arrayIndexScale(ak);
+            // ABASE absorbs padding in front of element 0
+            ABASE = U.arrayBaseOffset(ak) + (1 << ASHIFT);
+
+        } catch (Exception e) {
+            throw new Error(e);
         }
-        throw new InterruptedException();
+        if ((s & (s-1)) != 0 || s > (1 << ASHIFT))
+            throw new Error("Unsupported array scale");
     }
+
 }

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

@@ -46,7 +46,7 @@ import java.util.concurrent.locks.LockSupport;
  * {@link java.util.concurrent.CountDownLatch CountDownLatch}
  * but supporting more flexible usage.
  *
- * <p> <b>Registration.</b> Unlike the case for other barriers, the
+ * <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
@@ -59,7 +59,7 @@ import java.util.concurrent.locks.LockSupport;
  * (However, you can introduce such bookkeeping by subclassing this
  * class.)
  *
- * <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
+ * <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
@@ -103,7 +103,7 @@ import java.util.concurrent.locks.LockSupport;
  *
  * </ul>
  *
- * <p> <b>Termination.</b> A phaser may enter a <em>termination</em>
+ * <p><b>Termination.</b> A phaser may enter a <em>termination</em>
  * state, that may be checked using method {@link #isTerminated}. Upon
  * termination, all synchronization methods immediately return without
  * waiting for advance, as indicated by a negative return value.
@@ -118,7 +118,7 @@ import java.util.concurrent.locks.LockSupport;
  * also available to abruptly release waiting threads and allow them
  * to terminate.
  *
- * <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
+ * <p><b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
  * constructed 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
@@ -300,18 +300,20 @@ public class Phaser {
     private static final int  PHASE_SHIFT     = 32;
     private static final int  UNARRIVED_MASK  = 0xffff;      // to mask ints
     private static final long PARTIES_MASK    = 0xffff0000L; // to mask longs
+    private static final long COUNTS_MASK     = 0xffffffffL;
     private static final long TERMINATION_BIT = 1L << 63;
 
     // some special values
     private static final int  ONE_ARRIVAL     = 1;
     private static final int  ONE_PARTY       = 1 << PARTIES_SHIFT;
+    private static final int  ONE_DEREGISTER  = ONE_ARRIVAL|ONE_PARTY;
     private static final int  EMPTY           = 1;
 
     // The following unpacking methods are usually manually inlined
 
     private static int unarrivedOf(long s) {
         int counts = (int)s;
-        return (counts == EMPTY) ? 0 : counts & UNARRIVED_MASK;
+        return (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
     }
 
     private static int partiesOf(long s) {
@@ -372,37 +374,44 @@ public class Phaser {
      * Manually tuned to speed up and minimize race windows for the
      * common case of just decrementing unarrived field.
      *
-     * @param deregister false for arrive, true for arriveAndDeregister
+     * @param adjust value to subtract from state;
+     *               ONE_ARRIVAL for arrive,
+     *               ONE_DEREGISTER for arriveAndDeregister
      */
-    private int doArrive(boolean deregister) {
-        int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL;
+    private int doArrive(int adjust) {
         final Phaser root = this.root;
         for (;;) {
             long s = (root == this) ? state : reconcileState();
             int phase = (int)(s >>> PHASE_SHIFT);
-            int counts = (int)s;
-            int unarrived = (counts & UNARRIVED_MASK) - 1;
             if (phase < 0)
                 return phase;
-            else if (counts == EMPTY || unarrived < 0) {
-                if (root == this || reconcileState() == s)
-                    throw new IllegalStateException(badArrive(s));
-            }
-            else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
-                if (unarrived == 0) {
+            int counts = (int)s;
+            int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
+            if (unarrived <= 0)
+                throw new IllegalStateException(badArrive(s));
+            if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adjust)) {
+                if (unarrived == 1) {
                     long n = s & PARTIES_MASK;  // base of next state
                     int nextUnarrived = (int)n >>> PARTIES_SHIFT;
-                    if (root != this)
-                        return parent.doArrive(nextUnarrived == 0);
-                    if (onAdvance(phase, nextUnarrived))
-                        n |= TERMINATION_BIT;
-                    else if (nextUnarrived == 0)
-                        n |= EMPTY;
+                    if (root == this) {
+                        if (onAdvance(phase, nextUnarrived))
+                            n |= TERMINATION_BIT;
+                        else if (nextUnarrived == 0)
+                            n |= EMPTY;
+                        else
+                            n |= nextUnarrived;
+                        int nextPhase = (phase + 1) & MAX_PHASE;
+                        n |= (long)nextPhase << PHASE_SHIFT;
+                        UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
+                        releaseWaiters(phase);
+                    }
+                    else if (nextUnarrived == 0) { // propagate deregistration
+                        phase = parent.doArrive(ONE_DEREGISTER);
+                        UNSAFE.compareAndSwapLong(this, stateOffset,
+                                                  s, s | EMPTY);
+                    }
                     else
-                        n |= nextUnarrived;
-                    n |= (long)((phase + 1) & MAX_PHASE) << PHASE_SHIFT;
-                    UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
-                    releaseWaiters(phase);
+                        phase = parent.doArrive(ONE_ARRIVAL);
                 }
                 return phase;
             }
@@ -417,42 +426,49 @@ public class Phaser {
      */
     private int doRegister(int registrations) {
         // adjustment to state
-        long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
+        long adjust = ((long)registrations << PARTIES_SHIFT) | registrations;
         final Phaser parent = this.parent;
         int phase;
         for (;;) {
-            long s = state;
+            long s = (parent == null) ? state : reconcileState();
             int counts = (int)s;
             int parties = counts >>> PARTIES_SHIFT;
             int unarrived = counts & UNARRIVED_MASK;
             if (registrations > MAX_PARTIES - parties)
                 throw new IllegalStateException(badRegister(s));
-            else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0)
+            phase = (int)(s >>> PHASE_SHIFT);
+            if (phase < 0)
                 break;
-            else if (counts != EMPTY) {             // not 1st registration
+            if (counts != EMPTY) {                  // not 1st registration
                 if (parent == null || reconcileState() == s) {
                     if (unarrived == 0)             // wait out advance
                         root.internalAwaitAdvance(phase, null);
                     else if (UNSAFE.compareAndSwapLong(this, stateOffset,
-                                                       s, s + adj))
+                                                       s, s + adjust))
                         break;
                 }
             }
             else if (parent == null) {              // 1st root registration
-                long next = ((long)phase << PHASE_SHIFT) | adj;
+                long next = ((long)phase << PHASE_SHIFT) | adjust;
                 if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
                     break;
             }
             else {
                 synchronized (this) {               // 1st sub registration
                     if (state == s) {               // recheck under lock
-                        parent.doRegister(1);
-                        do {                        // force current phase
+                        phase = parent.doRegister(1);
+                        if (phase < 0)
+                            break;
+                        // finish registration whenever parent registration
+                        // succeeded, even when racing with termination,
+                        // since these are part of the same "transaction".
+                        while (!UNSAFE.compareAndSwapLong
+                               (this, stateOffset, s,
+                                ((long)phase << PHASE_SHIFT) | adjust)) {
+                            s = state;
                             phase = (int)(root.state >>> PHASE_SHIFT);
-                            // assert phase < 0 || (int)state == EMPTY;
-                        } while (!UNSAFE.compareAndSwapLong
-                                 (this, stateOffset, state,
-                                  ((long)phase << PHASE_SHIFT) | adj));
+                            // assert (int)s == EMPTY;
+                        }
                         break;
                     }
                 }
@@ -467,10 +483,6 @@ public class Phaser {
      * subphasers have not yet done so, in which case they must finish
      * their own advance by setting unarrived to parties (or if
      * parties is zero, resetting to unregistered EMPTY state).
-     * However, this method may also be called when "floating"
-     * subphasers with possibly some unarrived parties are merely
-     * catching up to current phase, in which case counts are
-     * unaffected.
      *
      * @return reconciled state
      */
@@ -478,16 +490,16 @@ public class Phaser {
         final Phaser root = this.root;
         long s = state;
         if (root != this) {
-            int phase, u, p;
-            // CAS root phase with current parties; possibly trip unarrived
+            int phase, p;
+            // CAS to root phase with current parties, tripping unarrived
             while ((phase = (int)(root.state >>> PHASE_SHIFT)) !=
                    (int)(s >>> PHASE_SHIFT) &&
                    !UNSAFE.compareAndSwapLong
                    (this, stateOffset, s,
                     s = (((long)phase << PHASE_SHIFT) |
-                         (s & PARTIES_MASK) |
-                         ((p = (int)s >>> PARTIES_SHIFT) == 0 ? EMPTY :
-                          (u = (int)s & UNARRIVED_MASK) == 0 ? p : u))))
+                         ((phase < 0) ? (s & COUNTS_MASK) :
+                          (((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY :
+                           ((s & PARTIES_MASK) | p))))))
                 s = state;
         }
         return s;
@@ -619,7 +631,7 @@ public class Phaser {
      * of unarrived parties would become negative
      */
     public int arrive() {
-        return doArrive(false);
+        return doArrive(ONE_ARRIVAL);
     }
 
     /**
@@ -639,7 +651,7 @@ public class Phaser {
      * of registered or unarrived parties would become negative
      */
     public int arriveAndDeregister() {
-        return doArrive(true);
+        return doArrive(ONE_DEREGISTER);
     }
 
     /**
@@ -666,17 +678,15 @@ public class Phaser {
         for (;;) {
             long s = (root == this) ? state : reconcileState();
             int phase = (int)(s >>> PHASE_SHIFT);
-            int counts = (int)s;
-            int unarrived = (counts & UNARRIVED_MASK) - 1;
             if (phase < 0)
                 return phase;
-            else if (counts == EMPTY || unarrived < 0) {
-                if (reconcileState() == s)
-                    throw new IllegalStateException(badArrive(s));
-            }
-            else if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
-                                               s -= ONE_ARRIVAL)) {
-                if (unarrived != 0)
+            int counts = (int)s;
+            int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
+            if (unarrived <= 0)
+                throw new IllegalStateException(badArrive(s));
+            if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
+                                          s -= ONE_ARRIVAL)) {
+                if (unarrived > 1)
                     return root.internalAwaitAdvance(phase, null);
                 if (root != this)
                     return parent.arriveAndAwaitAdvance();
@@ -809,8 +819,8 @@ public class Phaser {
             if (UNSAFE.compareAndSwapLong(root, stateOffset,
                                           s, s | TERMINATION_BIT)) {
                 // signal all threads
-                releaseWaiters(0);
-                releaseWaiters(1);
+                releaseWaiters(0); // Waiters on evenQ
+                releaseWaiters(1); // Waiters on oddQ
                 return;
             }
         }
@@ -1016,7 +1026,7 @@ public class Phaser {
 
     /**
      * Possibly blocks and waits for phase to advance unless aborted.
-     * Call only from root node.
+     * Call only on root phaser.
      *
      * @param phase current phase
      * @param node if non-null, the wait node to track interrupt and timeout;
@@ -1024,6 +1034,7 @@ public class Phaser {
      * @return current phase
      */
     private int internalAwaitAdvance(int phase, QNode node) {
+        // assert root == this;
         releaseWaiters(phase-1);          // ensure old queue clean
         boolean queued = false;           // true when node is enqueued
         int lastUnarrived = 0;            // to increase spins upon change
@@ -1082,7 +1093,7 @@ public class Phaser {
         final boolean timed;
         boolean wasInterrupted;
         long nanos;
-        long lastTime;
+        final long deadline;
         volatile Thread thread; // nulled to cancel wait
         QNode next;
 
@@ -1093,7 +1104,7 @@ public class Phaser {
             this.interruptible = interruptible;
             this.nanos = nanos;
             this.timed = timed;
-            this.lastTime = timed ? System.nanoTime() : 0L;
+            this.deadline = timed ? System.nanoTime() + nanos : 0L;
             thread = Thread.currentThread();
         }
 
@@ -1112,9 +1123,7 @@ public class Phaser {
             }
             if (timed) {
                 if (nanos > 0L) {
-                    long now = System.nanoTime();
-                    nanos -= now - lastTime;
-                    lastTime = now;
+                    nanos = deadline - System.nanoTime();
                 }
                 if (nanos <= 0L) {
                     thread = null;
@@ -1129,7 +1138,7 @@ public class Phaser {
                 return true;
             else if (!timed)
                 LockSupport.park(this);
-            else if (nanos > 0)
+            else if (nanos > 0L)
                 LockSupport.parkNanos(this, nanos);
             return isReleasable();
         }

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

@@ -36,10 +36,10 @@
 package java.util.concurrent;
 
 /**
- * A <tt>TimeUnit</tt> represents time durations at a given unit of
+ * A {@code TimeUnit} represents time durations at a given unit of
  * granularity and provides utility methods to convert across units,
  * and to perform timing and delay operations in these units.  A
- * <tt>TimeUnit</tt> does not maintain time information, but only
+ * {@code TimeUnit} does not maintain time information, but only
  * helps organize and use time representations that may be maintained
  * separately across various contexts.  A nanosecond is defined as one
  * thousandth of a microsecond, a microsecond as one thousandth of a
@@ -47,7 +47,7 @@ package java.util.concurrent;
  * as sixty seconds, an hour as sixty minutes, and a day as twenty four
  * hours.
  *
- * <p>A <tt>TimeUnit</tt> is mainly used to inform time-based methods
+ * <p>A {@code TimeUnit} is mainly used to inform time-based methods
  * how a given timing parameter should be interpreted. For example,
  * the following code will timeout in 50 milliseconds if the {@link
  * java.util.concurrent.locks.Lock lock} is not available:
@@ -63,7 +63,7 @@ package java.util.concurrent;
  *
  * Note however, that there is no guarantee that a particular timeout
  * implementation will be able to notice the passage of time at the
- * same granularity as the given <tt>TimeUnit</tt>.
+ * same granularity as the given {@code TimeUnit}.
  *
  * @since 1.5
  * @author Doug Lea
@@ -174,83 +174,82 @@ public enum TimeUnit {
     // etc. are not declared abstract but otherwise act as abstract methods.
 
     /**
-     * Convert the given time duration in the given unit to this
-     * unit.  Conversions from finer to coarser granularities
-     * truncate, so lose precision. For example converting
-     * <tt>999</tt> milliseconds to seconds results in
-     * <tt>0</tt>. Conversions from coarser to finer granularities
-     * with arguments that would numerically overflow saturate to
-     * <tt>Long.MIN_VALUE</tt> if negative or <tt>Long.MAX_VALUE</tt>
-     * if positive.
+     * Converts the given time duration in the given unit to this unit.
+     * Conversions from finer to coarser granularities truncate, so
+     * lose precision. For example, converting {@code 999} milliseconds
+     * to seconds results in {@code 0}. Conversions from coarser to
+     * finer granularities with arguments that would numerically
+     * overflow saturate to {@code Long.MIN_VALUE} if negative or
+     * {@code Long.MAX_VALUE} if positive.
      *
      * <p>For example, to convert 10 minutes to milliseconds, use:
-     * <tt>TimeUnit.MILLISECONDS.convert(10L, TimeUnit.MINUTES)</tt>
+     * {@code TimeUnit.MILLISECONDS.convert(10L, TimeUnit.MINUTES)}
      *
-     * @param sourceDuration the time duration in the given <tt>sourceUnit</tt>
-     * @param sourceUnit the unit of the <tt>sourceDuration</tt> argument
+     * @param sourceDuration the time duration in the given {@code sourceUnit}
+     * @param sourceUnit the unit of the {@code sourceDuration} argument
      * @return the converted duration in this unit,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      */
     public long convert(long sourceDuration, TimeUnit sourceUnit) {
         throw new AbstractMethodError();
     }
 
     /**
-     * Equivalent to <tt>NANOSECONDS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) NANOSECONDS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      */
     public long toNanos(long duration) {
         throw new AbstractMethodError();
     }
 
     /**
-     * Equivalent to <tt>MICROSECONDS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) MICROSECONDS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      */
     public long toMicros(long duration) {
         throw new AbstractMethodError();
     }
 
     /**
-     * Equivalent to <tt>MILLISECONDS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) MILLISECONDS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      */
     public long toMillis(long duration) {
         throw new AbstractMethodError();
     }
 
     /**
-     * Equivalent to <tt>SECONDS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) SECONDS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      */
     public long toSeconds(long duration) {
         throw new AbstractMethodError();
     }
 
     /**
-     * Equivalent to <tt>MINUTES.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) MINUTES.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      * @since 1.6
      */
     public long toMinutes(long duration) {
@@ -258,12 +257,12 @@ public enum TimeUnit {
     }
 
     /**
-     * Equivalent to <tt>HOURS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) HOURS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration,
-     * or <tt>Long.MIN_VALUE</tt> if conversion would negatively
-     * overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
-     * @see #convert
+     * or {@code Long.MIN_VALUE} if conversion would negatively
+     * overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
      * @since 1.6
      */
     public long toHours(long duration) {
@@ -271,10 +270,10 @@ public enum TimeUnit {
     }
 
     /**
-     * Equivalent to <tt>DAYS.convert(duration, this)</tt>.
+     * Equivalent to
+     * {@link #convert(long, TimeUnit) DAYS.convert(duration, this)}.
      * @param duration the duration
      * @return the converted duration
-     * @see #convert
      * @since 1.6
      */
     public long toDays(long duration) {
@@ -294,9 +293,9 @@ public enum TimeUnit {
      * Performs a timed {@link Object#wait(long, int) Object.wait}
      * using this time unit.
      * This is a convenience method that converts timeout arguments
-     * into the form required by the <tt>Object.wait</tt> method.
+     * into the form required by the {@code Object.wait} method.
      *
-     * <p>For example, you could implement a blocking <tt>poll</tt>
+     * <p>For example, you could implement a blocking {@code poll}
      * method (see {@link BlockingQueue#poll BlockingQueue.poll})
      * using:
      *
@@ -327,7 +326,7 @@ public enum TimeUnit {
      * Performs a timed {@link Thread#join(long, int) Thread.join}
      * using this time unit.
      * This is a convenience method that converts time arguments into the
-     * form required by the <tt>Thread.join</tt> method.
+     * form required by the {@code Thread.join} method.
      *
      * @param thread the thread to wait for
      * @param timeout the maximum time to wait. If less than
@@ -347,7 +346,7 @@ public enum TimeUnit {
      * Performs a {@link Thread#sleep(long, int) Thread.sleep} using
      * this time unit.
      * This is a convenience method that converts time arguments into the
-     * form required by the <tt>Thread.sleep</tt> method.
+     * form required by the {@code Thread.sleep} method.
      *
      * @param timeout the minimum time to sleep. If less than
      * or equal to zero, do not sleep at all.

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

@@ -40,7 +40,7 @@ package java.util.concurrent;
  * operations for which a timeout is specified need a means to
  * indicate that the timeout has occurred. For many such operations it
  * is possible to return a value that indicates timeout; when that is
- * not possible or desirable then <tt>TimeoutException</tt> should be
+ * not possible or desirable then {@code TimeoutException} should be
  * declared and thrown.
  *
  * @since 1.5
@@ -50,13 +50,13 @@ public class TimeoutException extends Exception {
     private static final long serialVersionUID = 1900926677490660714L;
 
     /**
-     * Constructs a <tt>TimeoutException</tt> with no specified detail
+     * Constructs a {@code TimeoutException} with no specified detail
      * message.
      */
     public TimeoutException() {}
 
     /**
-     * Constructs a <tt>TimeoutException</tt> with the specified detail
+     * Constructs a {@code TimeoutException} with the specified detail
      * message.
      *
      * @param message the detail message

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

@@ -48,7 +48,7 @@
  *
  * {@link java.util.concurrent.Executor} is a simple standardized
  * interface for defining custom thread-like subsystems, including
- * thread pools, asynchronous IO, and lightweight task frameworks.
+ * thread pools, asynchronous I/O, and lightweight task frameworks.
  * Depending on which concrete Executor class is being used, tasks may
  * execute in a newly created thread, an existing task-execution thread,
  * or the thread calling {@link java.util.concurrent.Executor#execute
@@ -102,8 +102,10 @@
  * <h2>Queues</h2>
  *
  * The {@link java.util.concurrent.ConcurrentLinkedQueue} class
- * supplies an efficient scalable thread-safe non-blocking FIFO
- * queue.
+ * supplies an efficient scalable thread-safe non-blocking FIFO queue.
+ * The {@link java.util.concurrent.ConcurrentLinkedDeque} class is
+ * similar, but additionally supports the {@link java.util.Deque}
+ * interface.
  *
  * <p>Five implementations in {@code java.util.concurrent} support
  * the extended {@link java.util.concurrent.BlockingQueue}
@@ -117,7 +119,7 @@
  * for producer-consumer, messaging, parallel tasking, and
  * related concurrent designs.
  *
- * <p> Extended interface {@link java.util.concurrent.TransferQueue},
+ * <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
@@ -216,9 +218,9 @@
  * it may (or may not) reflect any updates since the iterator was
  * created.
  *
- * <h2><a name="MemoryVisibility">Memory Consistency Properties</a></h2>
+ * <h2 id="MemoryVisibility">Memory Consistency Properties</h2>
  *
- * <a href="http://docs.oracle.com/javase/specs/jls/se7/html/index.html">
+ * <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.4.5">
  * Chapter 17 of the Java Language Specification</a> defines the
  * <i>happens-before</i> relation on memory operations such as reads and
  * writes of shared variables.  The results of a write by one thread are