RunQueue


1   // $Id: RunQueue.java,v 1.2 2001/12/07 11:41:24 ramsdell Exp $
2   
3   // A queue for runnable tasks
4   
5   /*
6    * Copyright 1998 by John D. Ramsdell
7    *
8    * This program is free software; you can redistribute it and/or
9    * modify it under the terms of the GNU Lesser General Public License
10   * as published by the Free Software Foundation; either version 2
11   * of the License, or (at your option) any later version.
12   *
13   * This program is distributed in the hope that it will be useful,
14   * but WITHOUT ANY WARRANTY; without even the implied warranty of
15   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16   * GNU Lesser General Public License for more details.
17   *
18   * You should have received a copy of the GNU Lesser General Public License
19   * along with this program; if not, write to the Free Software
20   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21   */
22  
23  package edu.neu.ccs.jmk.awt;
24  
25  import java.util.Vector  ;
26  
27  /**
28   * A queue for runnable tasks.
29   * The run method sequentially invokes tasks in the queue.
30   * The run queue is meant to be run in its own thread.
31   * @version January 1998
32   * @author John D. Ramsdell
33   */
34  public class RunQueue
35  implements Runnable  
36  {
37    // A queue of runnables
38    private final Vector   queue = new Vector  ();
39  
40    // Indicates that tasks extracted from the queue should not be started
41    private volatile boolean interrupt = false;
42  
43    // Indicates that the run method should exit
44    private volatile boolean poisoned = false;
45  
46    /**
47     * Stop the run method.
48     * To stop the run method, poison it,
49     * and then interrupt the thread running it.
50     */
51    public void setPoisoned(boolean poisoned) {
52      this.poisoned = poisoned;
53    }
54  
55    /**
56     * Add a task to the run queue.
57     * @param task a runnable task
58     */
59    public synchronized void add(Runnable   task) {
60      queue.addElement(task);
61      notify();
62    }
63  
64    /**
65     * Remove all tasks from the run queue.
66     */
67    public synchronized void removeAll() {
68      interrupt = true;       // Stop all tasks that
69      queue.removeAllElements();  // have not been started
70    }
71  
72    /**
73     * Runs tasks in a task queue.
74     */
75    public void run() {
76      Vector   q;
77      while (!poisoned) {
78        try {
79      synchronized (this) {
80        while (queue.isEmpty())
81          wait();
82        q = (Vector  )queue.clone(); // Extract tasks from the queue
83        queue.removeAllElements();
84        interrupt = false;
85      }
86        }
87        catch (InterruptedException   ie) {
88      continue;       // q is null so just continue loop
89        }
90        // Abort loop when the interrupt is enabled
91        for (int i = 0; i < q.size() && !interrupt; i++) {
92      Runnable   task = (Runnable  )q.elementAt(i);
93      try {
94        task.run();
95      }
96      catch (Throwable   t) {
97        System.err.println("Internal error: " + t.getMessage());
98        t.printStackTrace();
99      }
100       }
101       q = null;         // Recycle queue.
102     }
103   }
104 }
105
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