1/*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 */
22
23/*
24 * This file is available under and governed by the GNU General Public
25 * License version 2 only, as published by the Free Software Foundation.
26 * However, the following notice accompanied the original version of this
27 * file:
28 *
29 * Written by Doug Lea with assistance from members of JCP JSR-166
30 * Expert Group and released to the public domain, as explained at
31 * http://creativecommons.org/publicdomain/zero/1.0/
32 */
33
34import java.util.concurrent.TimeUnit;
35import java.util.concurrent.locks.AbstractQueuedSynchronizer;
36import java.util.concurrent.locks.Condition;
37import java.util.concurrent.locks.Lock;
38import java.io.IOException;
39import java.io.ObjectInputStream;
40
41/**
42 * A sample user extension of AbstractQueuedSynchronizer.
43 */
44public class Mutex implements Lock, java.io.Serializable {
45    private static class Sync extends AbstractQueuedSynchronizer {
46        public boolean isHeldExclusively() { return getState() == 1; }
47
48        public boolean tryAcquire(int acquires) {
49            assert acquires == 1; // Does not use multiple acquires
50            return compareAndSetState(0, 1);
51        }
52
53        public boolean tryRelease(int releases) {
54            setState(0);
55            return true;
56        }
57
58        Condition newCondition() { return new ConditionObject(); }
59
60        private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
61            s.defaultReadObject();
62            setState(0); // reset to unlocked state
63        }
64    }
65
66    private final Sync sync = new Sync();
67    public void lock() {
68        sync.acquire(1);
69    }
70    public boolean tryLock() {
71        return sync.tryAcquire(1);
72    }
73    public void lockInterruptibly() throws InterruptedException {
74        sync.acquireInterruptibly(1);
75    }
76    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
77        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
78    }
79    public void unlock() { sync.release(1); }
80    public Condition newCondition() { return sync.newCondition(); }
81    public boolean isLocked() { return sync.isHeldExclusively(); }
82    public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }
83}
84