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   * <p>
27   * Registry for {@link ReadWriteLock} objects with {@link ReadWriteLockKey} as
28   * keys. The behavior of acquiring and releasing locks is provided by a {@link
29   * ConcurrentHashMap}. This class is completely thread safe and ensures that
30   * only one {@link ReadWriteLock} exists per key.
31   * </p>
32   *
33   * @author Shuyang Zhou
34   * @see    ReadWriteLock
35   * @see    ReadWriteLockKey
36   */
37  public class ReadWriteLockRegistry {
38  
39      public Lock acquireLock(ReadWriteLockKey<?> readWriteLockKey) {
40          ReadWriteLock readWriteLock = _readWriteLockMap.get(readWriteLockKey);
41  
42          if (readWriteLock == null) {
43              ReadWriteLock newReadWriteLock = new ReentrantReadWriteLock();
44  
45              readWriteLock = _readWriteLockMap.putIfAbsent(
46                  readWriteLockKey, newReadWriteLock);
47  
48              if (readWriteLock == null) {
49                  readWriteLock = newReadWriteLock;
50              }
51          }
52  
53          if (readWriteLockKey.isWriteLock()) {
54              return readWriteLock.writeLock();
55          }
56          else {
57              return readWriteLock.readLock();
58          }
59      }
60  
61      public void releaseLock(ReadWriteLockKey<?> readWriteLockKey) {
62          if (readWriteLockKey.isWriteLock()) {
63              _readWriteLockMap.remove(readWriteLockKey);
64          }
65      }
66  
67      private ConcurrentMap<ReadWriteLockKey<?>, ReadWriteLock>
68          _readWriteLockMap = new ConcurrentHashMap
69              <ReadWriteLockKey<?>, ReadWriteLock>();
70  
71  }