ThreadWorker


1   // You can redistribute this software and/or modify it under the terms of
2   // the Ozone Library License version 1 published by ozone-db.org.
3   //
4   // The original code and portions created by SMB are
5   // Copyright (C) 1997-@year@ by SMB GmbH. All rights reserved.
6   //
7   // $Id: ThreadWorker.java,v 1.1 2003/03/07 13:49:45 per_nyfelt Exp $
8   package org.ozoneDB.adminGui.util;
9   
10  import javax.swing.*;
11  
12  /**
13   * ThreadWorker, an abstract class that you subclass to
14   * perform GUI-related work in a dedicated thread.
15   *
16   */
17  public abstract class ThreadWorker {
18      private Object   value;
19      private ThreadVar threadVar;
20  
21      /**
22       * Class to maintain reference to current worker thread
23       * under separate synchronization control.
24       */
25      private static class ThreadVar {
26          private Thread   thread;
27  
28          ThreadVar(Thread   t) {
29              thread = t;
30          }
31  
32          synchronized Thread   get() {
33              return thread;
34          }
35  
36          synchronized void clear() {
37              thread = null;
38          }
39      }
40  
41      /**
42       * Get the value produced by the worker thread, or null if it
43       * hasn't been constructed yet.
44       */
45      protected synchronized Object   getValue() {
46          return value;
47      }
48  
49      /**
50       * Set the value produced by worker thread
51       */
52      private synchronized void setValue(Object   x) {
53          value = x;
54      }
55  
56      /**
57       * Compute the value to be returned by the <code>get</code> method.
58       */
59      public abstract Object   construct();
60  
61      /**
62       * Called on the event dispatching thread (not on the worker thread)
63       * after the <code>construct</code> method has returned.
64       */
65      public void finished() {
66      }
67  
68      /**
69       * A new method that interrupts the worker thread.  Call this method
70       * to force the worker to stop what it's doing.
71       */
72      public void interrupt() {
73          Thread   t = threadVar.get();
74          if (t != null) {
75              t.interrupt();
76          }
77          threadVar.clear();
78      }
79  
80      /**
81       * Return the value created by the <code>construct</code> method.
82       * Returns null if either the constructing thread or the current
83       * thread was interrupted before a value was produced.
84       *
85       * @return the value created by the <code>construct</code> method
86       */
87      public Object   get() {
88          while (true) {
89              Thread   t = threadVar.get();
90              if (t == null) {
91                  return getValue();
92              }
93              try {
94                  t.join();
95              } catch (InterruptedException   e) {
96                  Thread.currentThread().interrupt(); // propagate
97                  return null;
98              }
99          }
100     }
101 
102 
103     /**
104      * Start a thread that will call the <code>construct</code> method
105      * and then exit.
106      */
107     public ThreadWorker() {
108         final Runnable   doFinished = new Runnable  () {
109             public void run() {
110                 finished();
111             }
112         };
113 
114         Runnable   doConstruct = new Runnable  () {
115             public void run() {
116                 try {
117                     setValue(construct());
118                 } finally {
119                     threadVar.clear();
120                 }
121 
122                 SwingUtilities.invokeLater(doFinished);
123             }
124         };
125 
126         Thread   t = new Thread  (doConstruct);
127         threadVar = new ThreadVar(t);
128     }
129 
130     /**
131      * Start the worker thread.
132      */
133     public void start() {
134         Thread   t = threadVar.get();
135         if (t != null) {
136             t.start();
137         }
138     }
139 }
140
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