/*

 * 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

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 * 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);

        }

    }

}