SwingWorker


1   /**
2    * $RCSfile: SwingWorker.java,v $
3    * $Revision: 1.3 $
4    * $Date: 2005/03/07 07:31:50 $
5    *
6    * Copyright (C) 2004 Jive Software. All rights reserved.
7    *
8    * This software is published under the terms of the GNU Public License (GPL),
9    * a copy of which is included in this distribution.
10   */
11  
12  package org.jivesoftware.messenger.launcher;
13  
14  import javax.swing.SwingUtilities  ;
15  
16  /**
17   * Modified SwingWorker that actually works.
18   * @author Derek DeMoro
19   */
20  public abstract class SwingWorker {
21      private Object   value;  // see getValue(), setValue()
22      private Thread   thread;
23  
24      /**
25       * Class to maintain reference to current worker thread
26       * under separate synchronization control.
27       */
28      private static class ThreadVar {
29          private Thread   thread;
30  
31          ThreadVar(Thread   t) {
32              thread = t;
33          }
34  
35          synchronized Thread   get() {
36              return thread;
37          }
38  
39          synchronized void clear() {
40              thread = null;
41          }
42      }
43  
44      private ThreadVar threadVar;
45  
46      /**
47       * Get the value produced by the worker thread, or null if it
48       * hasn't been constructed yet.
49       */
50      protected synchronized Object   getValue() {
51          return value;
52      }
53  
54      /**
55       * Set the value produced by worker thread
56       */
57      private synchronized void setValue(Object   x) {
58          value = x;
59      }
60  
61      /**
62       * Compute the value to be returned by the <code>get</code> method.
63       */
64      public abstract Object   construct();
65  
66      /**
67       * Called on the event dispatching thread (not on the worker thread)
68       * after the <code>construct</code> method has returned.
69       */
70      public void finished() {
71  
72      }
73  
74      /**
75       * A new method that interrupts the worker thread.  Call this method
76       * to force the worker to stop what it's doing.
77       */
78      public void interrupt() {
79          Thread   t = threadVar.get();
80          if (t != null) {
81              t.interrupt();
82          }
83          threadVar.clear();
84      }
85  
86  
87      /**
88       * Return the value created by the <code>construct</code> method.
89       * Returns null if either the constructing thread or the current
90       * thread was interrupted before a value was produced.
91       *
92       * @return the value created by the <code>construct</code> method
93       */
94      public Object   get() {
95          while (true) {
96              Thread   t = threadVar.get();
97              if (t == null) {
98                  return getValue();
99              }
100             try {
101                 t.join();
102             }
103             catch (InterruptedException   e) {
104                 Thread.currentThread().interrupt(); // propagate
105                 return null;
106             }
107         }
108     }
109 
110 
111     /**
112      * Start a thread that will call the <code>construct</code> method
113      * and then exit.
114      */
115     public SwingWorker() {
116         final Runnable   doFinished = new Runnable  () {
117             public void run() {
118                 finished();
119             }
120         };
121 
122         Runnable   doConstruct = new Runnable  () {
123             public void run() {
124                 try {
125                     setValue(construct());
126                 }
127                 finally {
128                     threadVar.clear();
129                 }
130                 SwingUtilities.invokeLater(new Runnable  () {
131                     public void run() {
132                         finished();
133                     }
134                 });
135 
136             }
137         };
138 
139         Thread   t = new Thread  (doConstruct);
140         threadVar = new ThreadVar(t);
141     }
142 
143     /**
144      * Start the worker thread.
145      */
146     public void start() {
147         Thread   t = threadVar.get();
148         if (t != null) {
149             t.start();
150         }
151     }
152     
153 
154 }
155 
156
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