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/*
* 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;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
/**
* 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.gc().
* 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();
}
// The main thread waits until the threads has started and give it a chance
// for the threads to block on the queue.remove(TIMEOUT) call
startedSignal.await();
Thread.sleep(TIMEOUT / 2);
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.nanoTime();
reference = queue.remove(TIMEOUT);
actual = NANOSECONDS.toMillis(System.nanoTime() - start);
} catch (InterruptedException ex) {
throw new RuntimeException(ex);
}
}
}
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