8023234: StampedLock serializes readers on writer unlock

Summary: Sync-up the fix from jsr166 CVS, signal more readers on writer unlock
Reviewed-by: martin, shade
Contributed-by: NDoug Lea <dl@cs.oswego.edu>

test/java/util/concurrent/locks/StampedLock/ReadersUnlockAfterWriteUnlock.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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @run main/othervm/timeout=60 ReadersUnlockAfterWriteUnlock
+ * @bug 8023234
+ * @summary StampedLock serializes readers on writer unlock
+ * @author Dmitry Chyuko
+ * @author Aleksey Shipilev
+ */
+
+import java.util.concurrent.CyclicBarrier;
+import java.util.concurrent.locks.StampedLock;
+
+public class ReadersUnlockAfterWriteUnlock {
+    static final int RNUM = 2;
+    static final StampedLock sl = new StampedLock();
+    static volatile boolean isDone;
+
+    static CyclicBarrier iterationStart = new CyclicBarrier(RNUM + 1);
+    static CyclicBarrier readersHaveLocks = new CyclicBarrier(RNUM);
+    static CyclicBarrier writerHasLock = new CyclicBarrier(RNUM + 1);
+
+    static class Reader extends Thread {
+        final String name;
+        Reader(String name) {
+            super();
+            this.name = name;
+        }
+        public void run() {
+            while (!isDone && !isInterrupted()) {
+                try {
+                    iterationStart.await();
+                    writerHasLock.await();
+                    long rs = sl.readLock();
+
+                    // single reader blocks here indefinitely if readers
+                    // are serialized
+                    readersHaveLocks.await();
+
+                    sl.unlockRead(rs);
+                } catch (Exception e) {
+                    throw new IllegalStateException(e);
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) throws InterruptedException {
+        for (int r = 0 ; r < RNUM; ++r) {
+            new Reader("r" + r).start();
+        }
+        int i;
+        for (i = 0; i < 1024; ++i) {
+            try {
+                iterationStart.await();
+                long ws = sl.writeLock();
+                writerHasLock.await();
+                Thread.sleep(10);
+                sl.unlockWrite(ws);
+            } catch (Exception e) {
+                throw new IllegalStateException(e);
+            }
+        }
+        isDone = true;
+    }
+
+}