LockPool


1   package com.quadcap.sql.lock;
2   
3   /* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
4    *
5    * This software is distributed under the Quadcap Free Software License.
6    * This software may be used or modified for any purpose, personal or
7    * commercial.  Open Source redistributions are permitted.  Commercial
8    * redistribution of larger works derived from, or works which bundle
9    * this software requires a "Commercial Redistribution License"; see
10   * http://www.quadcap.com/purchase.
11   *
12   * Redistributions qualify as "Open Source" under  one of the following terms:
13   *   
14   *    Redistributions are made at no charge beyond the reasonable cost of
15   *    materials and delivery.
16   *
17   *    Redistributions are accompanied by a copy of the Source Code or by an
18   *    irrevocable offer to provide a copy of the Source Code for up to three
19   *    years at the cost of materials and delivery.  Such redistributions
20   *    must allow further use, modification, and redistribution of the Source
21   *    Code under substantially the same terms as this license.
22   *
23   * Redistributions of source code must retain the copyright notices as they
24   * appear in each source code file, these license terms, and the
25   * disclaimer/limitation of liability set forth as paragraph 6 below.
26   *
27   * Redistributions in binary form must reproduce this Copyright Notice,
28   * these license terms, and the disclaimer/limitation of liability set
29   * forth as paragraph 6 below, in the documentation and/or other materials
30   * provided with the distribution.
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32   * The Software is provided on an "AS IS" basis.  No warranty is
33   * provided that the Software is free of defects, or fit for a
34   * particular purpose.  
35   *
36   * Limitation of Liability. Quadcap Software shall not be liable
37   * for any damages suffered by the Licensee or any third party resulting
38   * from use of the Software.
39   */
40  
41  import java.util.HashMap  ;
42  
43  import java.lang.ref.SoftReference  ;
44  
45  import com.quadcap.util.Debug;
46  
47  /**
48   * Cache of lock objects
49   *
50   * @author Stan Bailes
51   */
52  public class LockPool {
53      HashMap                       locks   = new HashMap  ();
54      
55      public LockPool() {
56      }
57      
58      public final Lock get(Lock parent, String   name) {
59          SoftReference   ref = (SoftReference  )locks.get(name);
60          Lock lock = null;
61          if (ref != null) {
62              Object   obj = ref.get();
63              if (obj != null) {
64                  lock = (Lock)obj;
65              } else {
66                  locks.remove(name); // lock was gc'ed.
67              }
68          }
69          if (lock == null) {
70              lock = new Lock();
71              lock.init(parent, name);
72              ref = new SoftReference  (lock);
73              locks.put(name, ref);
74          }
75          return lock;
76      }
77  }
78
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