--- old/src/java.base/share/classes/java/lang/ref/Reference.java	2016-03-19 00:16:19.665454803 +0100
+++ new/src/java.base/share/classes/java/lang/ref/Reference.java	2016-03-19 00:16:19.603455838 +0100
@@ -29,7 +29,6 @@
 import jdk.internal.HotSpotIntrinsicCandidate;
 import jdk.internal.misc.JavaLangRefAccess;
 import jdk.internal.misc.SharedSecrets;
-import jdk.internal.ref.Cleaner;
 
 /**
  * Abstract base class for reference objects.  This class defines the
@@ -116,7 +115,7 @@
      * as possible, allocate no new objects, and avoid calling user code.
      */
     private static class Lock { }
-    private static Lock lock = new Lock();
+    private static final Lock lock = new Lock();
 
 
     /* List of References waiting to be enqueued.  The collector adds
@@ -126,6 +125,15 @@
      */
     private static Reference<Object> pending = null;
 
+    /* Unhook phase counter. Guarded by the above lock object.
+     */
+    private static int unhookPhase;
+
+    /* Enqueue phase counter, guarded by its own lock object.
+     */
+    private static int enqueuePhase;
+    private static final Object enqueuePhaseLock = new Object();
+
     /* High-priority thread to enqueue pending References
      */
     private static class ReferenceHandler extends Thread {
@@ -139,11 +147,10 @@
         }
 
         static {
-            // pre-load and initialize InterruptedException and Cleaner classes
+            // pre-load and initialize InterruptedException class
             // so that we don't get into trouble later in the run loop if there's
-            // memory shortage while loading/initializing them lazily.
+            // memory shortage while loading/initializing it lazily.
             ensureClassInitialized(InterruptedException.class);
-            ensureClassInitialized(Cleaner.class);
         }
 
         ReferenceHandler(ThreadGroup g, String name) {
@@ -152,72 +159,90 @@
 
         public void run() {
             while (true) {
-                tryHandlePending(true);
+                enqueuePendingReferences();
             }
         }
     }
 
     /**
-     * Try handle pending {@link Reference} if there is one.<p>
-     * Return {@code true} as a hint that there might be another
-     * {@link Reference} pending or {@code false} when there are no more pending
-     * {@link Reference}s at the moment and the program can do some other
-     * useful work instead of looping.
-     *
-     * @param waitForNotify if {@code true} and there was no pending
-     *                      {@link Reference}, wait until notified from VM
-     *                      or interrupted; if {@code false}, return immediately
-     *                      when there is no pending {@link Reference}.
-     * @return {@code true} if there was a {@link Reference} pending and it
-     *         was processed, or we waited for notification and either got it
-     *         or thread was interrupted before being notified;
-     *         {@code false} otherwise.
-     */
-    static boolean tryHandlePending(boolean waitForNotify) {
-        Reference<Object> r;
-        Cleaner c;
+     * Enqueue a chunk of pending {@link Reference}s if GC has discovered any
+     * or wait for GC to discover and notify us and then enqueue them.
+     * <p>
+     * The unhookPhase and enqueuePhase counters are incremented as the chunk of
+     * pending References is unhooked and after it is enqueued respectively so
+     * that any waiters can find out when the references that were pending upon
+     * the call to {@link #awaitPendingReferencesEnqueued()} have been enqueued.
+     * <p>
+     * Guarantees given by {@link #awaitPendingReferencesEnqueued()} method can
+     * only be respected if this method is executed by a single thread -
+     * the ReferenceHandler thread.
+     */
+    static void enqueuePendingReferences() {
+        Reference<Object> p;
         try {
             synchronized (lock) {
-                if (pending != null) {
-                    r = pending;
-                    // 'instanceof' might throw OutOfMemoryError sometimes
-                    // so do this before un-linking 'r' from the 'pending' chain...
-                    c = r instanceof Cleaner ? (Cleaner) r : null;
-                    // unlink 'r' from 'pending' chain
-                    pending = r.discovered;
-                    r.discovered = null;
-                } else {
-                    // The waiting on the lock may cause an OutOfMemoryError
-                    // because it may try to allocate exception objects.
-                    if (waitForNotify) {
-                        lock.wait();
-                    }
-                    // retry if waited
-                    return waitForNotify;
+                while ((p = pending) == null) {
+                    lock.wait();
                 }
+                // unhook the whole chain of pending References at once
+                pending = null;
+                // increment the unhookPhase counter and notify waiters
+                unhookPhase++;
+                lock.notifyAll();
             }
         } catch (OutOfMemoryError x) {
-            // Give other threads CPU time so they hopefully drop some live references
-            // and GC reclaims some space.
-            // Also prevent CPU intensive spinning in case 'r instanceof Cleaner' above
-            // persistently throws OOME for some time...
+            // The waiting on the lock may cause an OutOfMemoryError
+            // because it may try to allocate InterruptedException object.
+            // Give other threads CPU time so they hopefully drop some live
+            // references and GC reclaims some space.
             Thread.yield();
-            // retry
-            return true;
+            return;
         } catch (InterruptedException x) {
-            // retry
-            return true;
+            return;
+        }
+
+        try {
+            // distribute unhooked pending references to their respective queues
+            while (p != null) {
+                Reference<Object> r = p;
+                p = r.discovered;
+                r.discovered = null;
+                ReferenceQueue<? super Object> q = r.queue;
+                if (q != ReferenceQueue.NULL) q.enqueue(r);
+            }
+        } finally {
+            // increment the enqueuePhase counter and notify waiters
+            synchronized (enqueuePhaseLock) {
+                enqueuePhase++;
+                enqueuePhaseLock.notifyAll();
+            }
         }
+    }
 
-        // Fast path for cleaners
-        if (c != null) {
-            c.clean();
-            return true;
+    /**
+     * Blocks until all Reference(s) that were pending at the time this method
+     * was called have been enqueued.
+     *
+     * @throws InterruptedException if the thread is interrupted while waiting.
+     */
+    static void awaitPendingReferencesEnqueued() throws InterruptedException {
+        int unhookPhaseSnapshot;
+        synchronized (lock) {
+            // wait for ReferenceHandler to unhook the chunk of pending references
+            while (pending != null) {
+                lock.wait();
+            }
+            // remember the phase when after our arrival the chunk of pending
+            // references has been unhooked
+            unhookPhaseSnapshot = unhookPhase;
         }
 
-        ReferenceQueue<? super Object> q = r.queue;
-        if (q != ReferenceQueue.NULL) q.enqueue(r);
-        return true;
+        synchronized (enqueuePhaseLock) {
+            // wait for ReferenceHandler to enqueue those references
+            while (unhookPhaseSnapshot - enqueuePhase > 0) {
+                enqueuePhaseLock.wait();
+            }
+        }
     }
 
     static {
@@ -236,8 +261,13 @@
         // provide access in SharedSecrets
         SharedSecrets.setJavaLangRefAccess(new JavaLangRefAccess() {
             @Override
-            public boolean tryHandlePendingReference() {
-                return tryHandlePending(false);
+            public void awaitPendingReferencesEnqueued() throws InterruptedException {
+                Reference.awaitPendingReferencesEnqueued();
+            }
+
+            @Override
+            public boolean cleanNextEnqueuedCleanable(Cleaner cleaner) {
+                return cleaner.cleanNextEnqueued();
             }
         });
     }