1   /**
2    * Copyright (c) 2000-2009 Liferay, Inc. All rights reserved.
3    *
4    *
5    *
6    *
7    * The contents of this file are subject to the terms of the Liferay Enterprise
8    * Subscription License ("License"). You may not use this file except in
9    * compliance with the License. You can obtain a copy of the License by
10   * contacting Liferay, Inc. See the License for the specific language governing
11   * permissions and limitations under the License, including but not limited to
12   * distribution rights of the Software.
13   *
14   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
17   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
20   * SOFTWARE.
21   */
22  
23  package com.liferay.portal.kernel.concurrent;
24  
25  import java.util.concurrent.ConcurrentHashMap;
26  import java.util.concurrent.ConcurrentMap;
27  import java.util.concurrent.locks.Lock;
28  import java.util.concurrent.locks.ReadWriteLock;
29  import java.util.concurrent.locks.ReentrantReadWriteLock;
30  
31  /**
32   * <a href="ReadWriteLockRegistry.java.html"><b><i>View Source</i></b></a>
33   *
34   * Registry for {@link ReadWriteLock} objects with {@link ReadWriteLockKey} as
35   * keys. The behavior of acquiring and releasing locks is provided by a {@link
36   * ConcurrentHashMap}. This class is completely thread safe and ensures that
37   * only one {@link ReadWriteLock} exists per key. <a
38   * href="ReadWriteLockRegistry.java.html"><b><i>View Source</i></b></a>
39   *
40   * @author Shuyang Zhou
41   * @see    ReadWriteLock
42   * @see    ReadWriteLockKey
43   */
44  public class ReadWriteLockRegistry {
45  
46      public Lock acquireLock(ReadWriteLockKey<?> readWriteLockKey) {
47          ReadWriteLock readWriteLock = _readWriteLockMap.get(readWriteLockKey);
48  
49          if (readWriteLock == null) {
50              ReadWriteLock newReadWriteLock = new ReentrantReadWriteLock();
51  
52              readWriteLock = _readWriteLockMap.putIfAbsent(
53                  readWriteLockKey, newReadWriteLock);
54  
55              if (readWriteLock == null) {
56                  readWriteLock = newReadWriteLock;
57              }
58          }
59  
60          if (readWriteLockKey.isWriteLock()) {
61              return readWriteLock.writeLock();
62          }
63          else {
64              return readWriteLock.readLock();
65          }
66      }
67  
68      public void releaseLock(ReadWriteLockKey<?> readWriteLockKey) {
69          if (readWriteLockKey.isWriteLock()) {
70              _readWriteLockMap.remove(readWriteLockKey);
71          }
72      }
73  
74      private ConcurrentMap<ReadWriteLockKey<?>, ReadWriteLock>
75          _readWriteLockMap = new ConcurrentHashMap
76              <ReadWriteLockKey<?>, ReadWriteLock>();
77  
78  }