Lock


1   /*******************************************************************************
2    * Copyright (c) 2000, 2005 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    *
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.swt.internal;
12  
13  /**
14   * Instance of this represent a recursive monitor.
15   */
16  public class Lock {
17      int count, waitCount;
18      Thread   owner;
19  
20  /**
21   * Locks the monitor and returns the lock count. If
22   * the lock is owned by another thread, wait until
23   * the lock is released.
24   * 
25   * @return the lock count
26   */
27  public int lock() {
28      synchronized (this) {
29          Thread   current = Thread.currentThread();
30          if (owner != current) {
31              waitCount++;
32              while (count > 0) {
33                  try {
34                      wait();
35                  } catch (InterruptedException   e) {
36                      /* Wait forever, just like synchronized blocks */
37                  }
38              }
39              --waitCount;
40              owner = current;
41          }
42          return ++count;
43      }
44  }
45  
46  /**
47   * Unlocks the monitor. If the current thread is not
48   * the monitor owner, do nothing.
49   */
50  public void unlock() {
51      synchronized (this) {
52          Thread   current = Thread.currentThread();
53          if (owner == current) {
54              if (--count == 0) {
55                  owner = null;
56                  if (waitCount > 0) notifyAll();
57              }
58          }
59      }
60  }
61  }
62
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