1 /*
   2  * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 
  24 /* @test
  25  * @bug 6853696
  26  * @summary ReferenceQueue#remove(timeout) should not return null before
  27  *          timeout is elapsed
  28  */
  29 
  30 import java.lang.InterruptedException;
  31 import java.lang.System;
  32 import java.lang.ref.Reference;
  33 import java.lang.ref.ReferenceQueue;
  34 import java.lang.ref.WeakReference;
  35 import java.util.concurrent.CountDownLatch;
  36 
  37 /**
  38  * In order to demonstrate the issue we make several threads (two appears to be sufficient)
  39  * to block in ReferenceQueue#remove(timeout) at the same time.
  40  * Then, we force a reference to be enqueued by setting its referent to null and calling System.gs().
  41  * One of the threads gets the reference returned from the remove().
  42  * The other threads get null:
  43  * 1) with bug:  this may happen before the specified timeout is elapsed,
  44  * 2) without bug:  this can only happen after the timeout is fully elapsed.
  45  */
  46 
  47 public class EarlyTimeout extends Thread {
  48 
  49     static final int THREADS_COUNT = 2;
  50     static final int TIMEOUT = 1000;
  51 
  52     static Object referent = new Object();
  53     static final ReferenceQueue<Object> queue = new ReferenceQueue<Object>();
  54     static final WeakReference<Object> weakReference = new WeakReference<Object>(referent, queue);
  55     static final CountDownLatch startedSignal = new CountDownLatch(THREADS_COUNT);
  56 
  57     long actual;
  58     Reference<?> reference;
  59 
  60     public static void main(String[] args) throws Exception {
  61         EarlyTimeout[] threads = new EarlyTimeout[THREADS_COUNT];
  62         for (int i = 0; i < THREADS_COUNT; ++i) {
  63             threads[i] = new EarlyTimeout();
  64             threads[i].start();
  65         }
  66         startedSignal.await();
  67         referent = null;
  68         System.gc();
  69         for (EarlyTimeout thread : threads) {
  70             thread.join();
  71         }
  72         if (weakReference.get() != null) {
  73             throw new RuntimeException("weakReference was not cleared");
  74         }
  75         int nonNullRefCount = 0;
  76         for (EarlyTimeout thread : threads) {
  77             if (thread.reference == null && thread.actual < TIMEOUT) {
  78                 throw new RuntimeException("elapsed time " + thread.actual
  79                         + " is less than timeout " + TIMEOUT);
  80             }
  81             if (thread.reference != null && thread.reference == weakReference) {
  82                 nonNullRefCount++;
  83             }
  84         }
  85         if (nonNullRefCount != 1) {
  86             throw new RuntimeException("more than one references were removed from queue");
  87         }
  88     }
  89 
  90     public void run() {
  91         try {
  92             startedSignal.countDown();
  93             long start = System.currentTimeMillis();
  94             reference = queue.remove(TIMEOUT);
  95             actual = System.currentTimeMillis() - start;
  96         } catch (InterruptedException ex) {
  97             throw new RuntimeException(ex);
  98         }
  99     }
 100 }