| ReadWriteLockRegistry.java |
1 /**
2 * Copyright (c) 2000-2010 Liferay, Inc. All rights reserved.
3 *
4 * This library is free software; you can redistribute it and/or modify it under
5 * the terms of the GNU Lesser General Public License as published by the Free
6 * Software Foundation; either version 2.1 of the License, or (at your option)
7 * any later version.
8 *
9 * This library is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
11 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
12 * details.
13 */
14
15 package com.liferay.portal.kernel.concurrent;
16
17 import java.util.concurrent.ConcurrentHashMap;
18 import java.util.concurrent.ConcurrentMap;
19 import java.util.concurrent.locks.Lock;
20 import java.util.concurrent.locks.ReadWriteLock;
21 import java.util.concurrent.locks.ReentrantReadWriteLock;
22
23 /**
24 * <a href="ReadWriteLockRegistry.java.html"><b><i>View Source</i></b></a>
25 *
26 * Registry for {@link ReadWriteLock} objects with {@link ReadWriteLockKey} as
27 * keys. The behavior of acquiring and releasing locks is provided by a {@link
28 * ConcurrentHashMap}. This class is completely thread safe and ensures that
29 * only one {@link ReadWriteLock} exists per key. <a
30 * href="ReadWriteLockRegistry.java.html"><b><i>View Source</i></b></a>
31 *
32 * @author Shuyang Zhou
33 * @see ReadWriteLock
34 * @see ReadWriteLockKey
35 */
36 public class ReadWriteLockRegistry {
37
38 public Lock acquireLock(ReadWriteLockKey<?> readWriteLockKey) {
39 ReadWriteLock readWriteLock = _readWriteLockMap.get(readWriteLockKey);
40
41 if (readWriteLock == null) {
42 ReadWriteLock newReadWriteLock = new ReentrantReadWriteLock();
43
44 readWriteLock = _readWriteLockMap.putIfAbsent(
45 readWriteLockKey, newReadWriteLock);
46
47 if (readWriteLock == null) {
48 readWriteLock = newReadWriteLock;
49 }
50 }
51
52 if (readWriteLockKey.isWriteLock()) {
53 return readWriteLock.writeLock();
54 }
55 else {
56 return readWriteLock.readLock();
57 }
58 }
59
60 public void releaseLock(ReadWriteLockKey<?> readWriteLockKey) {
61 if (readWriteLockKey.isWriteLock()) {
62 _readWriteLockMap.remove(readWriteLockKey);
63 }
64 }
65
66 private ConcurrentMap<ReadWriteLockKey<?>, ReadWriteLock>
67 _readWriteLockMap = new ConcurrentHashMap
68 <ReadWriteLockKey<?>, ReadWriteLock>();
69
70 }