SwingWorker


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33  
34  package edu.rice.cs.util.swing;
35  
36  import javax.swing.SwingUtilities  ;
37  
38  /**
39   * SwingWorker, adapted from Sun's Java Tutorial.
40   *
41   * This is the 3rd version of SwingWorker (also known as
42   * SwingWorker 3), an abstract class that you subclass to
43   * perform GUI-related work in a dedicated thread.  For
44   * instructions on using this class, see:
45   *
46   * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
47   *
48   * Note that the API changed slightly in the 3rd version:
49   * You must now invoke start() on the SwingWorker after
50   * creating it.
51   *
52   * @version $Id: SwingWorker.java 4033 2006-11-16 20:16:51Z rcartwright $
53   */
54  public abstract class SwingWorker {
55    private volatile Object   _value;  // see getValue(), setValue()
56  //  private Thread _thread;
57  
58    /**
59     * Class to maintain reference to current worker thread
60     * under separate synchronization control.
61     */
62    private static class ThreadVar {
63      private volatile Thread   _thread;
64      ThreadVar(Thread   t) { _thread = t; }
65      Thread   get() { return _thread; }
66      void clear() { _thread = null; }
67    }
68  
69    private volatile ThreadVar _threadVar;
70  
71    /** Gets the value produced by the worker thread, or null if it
72     *  hasn't been constructed yet.
73     */
74    protected Object   getValue() { return _value; }
75  
76    /** Sets the value produced by worker thread. */
77    private void setValue(Object   x) { _value = x; }
78  
79    /** Compute the value to be returned by the <code>get</code> method. */
80    public abstract Object   construct();
81  
82    /** Called on the event dispatching thread (not on the worker thread)
83     *  after the <code>construct</code> method has returned.
84     */
85    public void finished() { }
86  
87    /** A new method that interrupts the worker thread.  Call this method to force the worker to stop what it's doing. */
88    public void interrupt() {
89      Thread   t = _threadVar.get();
90      if (t != null) t.interrupt();
91      _threadVar.clear();
92    }
93  
94    /** Return the value created by the <code>construct</code> method.  Returns null if either the constructing thread 
95     *  or the current thread was interrupted before a value was produced.
96     *
97     * @return the value created by the <code>construct</code> method
98     */
99    public Object   get() {
100     while (true) {
101       Thread   t = _threadVar.get();
102       if (t == null) return getValue();
103       try { t.join(); }
104       catch (InterruptedException   e) {
105         Thread.currentThread().interrupt(); // propagate
106         return null;
107       }
108     }
109   }
110 
111   /** Start a thread that will call the <code>construct</code> method and then exit. */
112   public SwingWorker() {
113     final Runnable   doFinished = new Runnable  () {
114       public void run() { finished(); }
115     };
116 
117     Runnable   doConstruct = new Runnable  () {
118       public void run() {
119         try { setValue(construct()); }
120         catch (final RuntimeException   e) {
121           // Throw the exception in the event dispatching thread.
122           SwingUtilities.invokeLater(new Runnable  () { public void run() { throw e; } });
123           throw e;
124         }
125         catch (final Error   e) {
126           // Throw the error in the event dispatching thread.
127           SwingUtilities.invokeLater(new Runnable  () { public void run() { throw e; } });
128           throw e;
129         }
130         finally { _threadVar.clear(); }
131 
132         SwingUtilities.invokeLater(doFinished);
133       }
134     };
135 
136     Thread   t = new Thread  (doConstruct);
137     _threadVar = new ThreadVar(t);
138   }
139 
140   /** Start the worker thread. */
141   public void start() {
142     Thread   t = _threadVar.get();
143     if (t != null) t.start();
144   }
145 }
146
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