6853696: (ref) ReferenceQueue.remove(timeout) may return null even if timeout has not expired
Reviewed-by: mchung, mduigou, rriggs
--- a/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java Wed Feb 26 19:11:00 2014 -0800
+++ b/jdk/src/share/classes/java/lang/ref/ReferenceQueue.java Thu Feb 27 02:44:04 2014 +0400
@@ -138,11 +138,17 @@
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;
+ }
}
}
}
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/test/java/lang/ref/EarlyTimeout.java Thu Feb 27 02:44:04 2014 +0400
@@ -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);
+ }
+ }
+}