1    /* 
2     * Copyright (C) 1997 Luke Gorrie 
3     * 
4     * This library is free software; you can redistribute it and/or 
5     * modify it under the terms of the GNU Library General Public 
6     * License as published by the Free Software Foundation; either 
7     * version 2 of the License, or (at your option) any later version. 
8     * 
9     * This library is distributed in the hope that it will be useful, 
10    * but WITHOUT ANY WARRANTY; without even the implied warranty of 
11    * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
12    * Library General Public License for more details. 
13    * 
14    * You should have received a copy of the GNU Library General Public 
15    * License along with this library; if not, write to the 
16    * Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
17    * MA 02139, USA. 
18    */ 
19    
20   package javagroup.util; 
21    
22   import java.util.Vector; 
23    
24   /** 
25    * Class to represent a reference-counted resource.  The resource is 
26    * dispose()d when all "hard" references are released. 
27    * 
28    * @author Luke Gorrie 
29    */ 
30   public class Resource implements Disposable { 
31    
32       // Vector used to reference resources to prevent garbage collection 
33       private static Vector __resources; 
34    
35       /** 
36        * The number of registered references to this Resource. 
37        */ 
38       protected int _references; 
39    
40       /** 
41        * True if this resource is not to be disposed of. 
42        */ 
43       protected boolean _static; 
44    
45       protected Vector _disposalListeners; 
46    
47       protected Disposable _wrappedResource; 
48    
49       protected boolean _disposed = false; 
50    
51       public Resource() { 
52           _disposalListeners = new Vector(); 
53       } 
54    
55       public Resource(Disposable disposable) { 
56           this(); 
57           _wrappedResource = disposable; 
58       } 
59    
60       /** 
61        * Lock add a lock. * 
62        */ 
63       public synchronized void addLock() { 
64           _references++; 
65       } 
66    
67       /** 
68        * Release a lock. * 
69        */ 
70       public synchronized void releaseLock() { 
71           if (!_static) { 
72               _references--; 
73    
74               if (_references <= 0) 
75                   this.dispose(); 
76           } 
77       } 
78    
79       /** 
80        * Mark resource as 'static', so it will never be destroyed. * 
81        */ 
82       public synchronized void setStatic() { 
83           if (!_static) 
84               __resources.addElement(this); 
85           _static = true; 
86       } 
87    
88       /** 
89        * Release all locks and free resource. * 
90        */ 
91       public void unregister() { 
92    
93           if (__resources.contains(this)) 
94               __resources.removeElement(this); 
95       } 
96    
97       public void dispose() { 
98           if (_disposed) 
99               return; 
100   
101          if (_wrappedResource != null) { 
102              _wrappedResource.dispose(); 
103          } 
104          fireResourceDisposalEvent(); 
105          _disposalListeners.removeAllElements(); 
106          _disposed = true; 
107      } 
108   
109      public boolean isDisposed() { 
110          return _disposed; 
111      } 
112   
113      public void addDisposalListener(ResourceDisposalListener listener) { 
114          _disposalListeners.addElement(listener); 
115      } 
116   
117      public void removeDisposalListener(ResourceDisposalListener listener) { 
118          _disposalListeners.removeElement(listener); 
119      } 
120   
121      public void fireResourceDisposalEvent() { 
122          synchronized (_disposalListeners) { 
123              for (int i = 0; i < _disposalListeners.size(); i++) { 
124                  ResourceDisposalListener listener = (ResourceDisposalListener) 
125                          _disposalListeners.elementAt(i); 
126                  listener.resourceDisposed(this); 
127              } 
128          } 
129      } 
130   
131  } 
132   
133