6853696: (ref) ReferenceQueue.remove(timeout) may return null even if timeout has not expired

Reviewed-by: mchung, mduigou, rriggs

jdk/src/share/classes/java/lang/ref/ReferenceQueue.java

@@ -138,11 +138,17 @@ public class ReferenceQueue<T> {
         synchronized (lock) {
             Reference<? extends T> r = reallyPoll();
             if (r != null) return r;
+            long start = (timeout == 0) ? 0 : System.nanoTime();
             for (;;) {
                 lock.wait(timeout);
                 r = reallyPoll();
                 if (r != null) return r;
-                if (timeout != 0) return null;
+                if (timeout != 0) {
+                    long end = System.nanoTime();
+                    timeout -= (end - start) / 1000_000;
+                    if (timeout <= 0) return null;
+                    start = end;
+                }
             }
         }
     }

jdk/test/java/lang/ref/EarlyTimeout.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
+ * 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
+ * @bug 6853696
+ * @summary ReferenceQueue#remove(timeout) should not return null before
+ *          timeout is elapsed
+ */
+
+import java.lang.InterruptedException;
+import java.lang.System;
+import java.lang.ref.Reference;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.WeakReference;
+import java.util.concurrent.CountDownLatch;
+
+/**
+ * In order to demonstrate the issue we make several threads (two appears to be sufficient)
+ * to block in ReferenceQueue#remove(timeout) at the same time.
+ * Then, we force a reference to be enqueued by setting its referent to null and calling System.gs().
+ * One of the threads gets the reference returned from the remove().
+ * The other threads get null:
+ * 1) with bug:  this may happen before the specified timeout is elapsed,
+ * 2) without bug:  this can only happen after the timeout is fully elapsed.
+ */
+
+public class EarlyTimeout extends Thread {
+
+    static final int THREADS_COUNT = 2;
+    static final int TIMEOUT = 1000;
+
+    static Object referent = new Object();
+    static final ReferenceQueue<Object> queue = new ReferenceQueue<Object>();
+    static final WeakReference<Object> weakReference = new WeakReference<Object>(referent, queue);
+    static final CountDownLatch startedSignal = new CountDownLatch(THREADS_COUNT);
+
+    long actual;
+    Reference<?> reference;
+
+    public static void main(String[] args) throws Exception {
+        EarlyTimeout[] threads = new EarlyTimeout[THREADS_COUNT];
+        for (int i = 0; i < THREADS_COUNT; ++i) {
+            threads[i] = new EarlyTimeout();
+            threads[i].start();
+        }
+        startedSignal.await();
+        referent = null;
+        System.gc();
+        for (EarlyTimeout thread : threads) {
+            thread.join();
+        }
+        if (weakReference.get() != null) {
+            throw new RuntimeException("weakReference was not cleared");
+        }
+        int nonNullRefCount = 0;
+        for (EarlyTimeout thread : threads) {
+            if (thread.reference == null && thread.actual < TIMEOUT) {
+                throw new RuntimeException("elapsed time " + thread.actual
+                        + " is less than timeout " + TIMEOUT);
+            }
+            if (thread.reference != null && thread.reference == weakReference) {
+                nonNullRefCount++;
+            }
+        }
+        if (nonNullRefCount != 1) {
+            throw new RuntimeException("more than one references were removed from queue");
+        }
+    }
+
+    public void run() {
+        try {
+            startedSignal.countDown();
+            long start = System.currentTimeMillis();
+            reference = queue.remove(TIMEOUT);
+            actual = System.currentTimeMillis() - start;
+        } catch (InterruptedException ex) {
+            throw new RuntimeException(ex);
+        }
+    }
+}