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1   /***
2    * Redistribution and use of this software and associated documentation
3    * ("Software"), with or without modification, are permitted provided
4    * that the following conditions are met:
5    *
6    * 1. Redistributions of source code must retain copyright
7    *    statements and notices.  Redistributions must also contain a
8    *    copy of this document.
9    *
10   * 2. Redistributions in binary form must reproduce the
11   *    above copyright notice, this list of conditions and the
12   *    following disclaimer in the documentation and/or other
13   *    materials provided with the distribution.
14   *
15   * 3. The name "Exolab" must not be used to endorse or promote
16   *    products derived from this Software without prior written
17   *    permission of Exoffice Technologies.  For written permission,
18   *    please contact info@exolab.org.
19   *
20   * 4. Products derived from this Software may not be called "Exolab"
21   *    nor may "Exolab" appear in their names without prior written
22   *    permission of Exoffice Technologies. Exolab is a registered
23   *    trademark of Exoffice Technologies.
24   *
25   * 5. Due credit should be given to the Exolab Project
26   *    (http://www.exolab.org/).
27   *
28   * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29   * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
30   * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
31   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
32   * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
33   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
34   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
35   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
37   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
38   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
39   * OF THE POSSIBILITY OF SUCH DAMAGE.
40   *
41   * Copyright 2000 (C) Exoffice Technologies Inc. All Rights Reserved.
42   *
43   * $Id: BlockingWorkerQueue.java,v 1.4 2003/08/07 13:33:12 tanderson Exp $
44   *
45   * Date         Author  Changes
46   * 5/15/2001    jima    Created
47   */
48  
49  
50  package org.exolab.jms.util;
51  
52  import java.util.LinkedList;
53  
54  
55  /***
56   * A BlockingWorkerQueue is attached to a QueueWorker. Any thread can add
57   * work to the queue. The BlockingWorkerQueue, which extends Thread, blocks
58   * waiting for work to arrive. When work arrives it will be dequeued and
59   * passed down to the QueueWorker for processing.
60   * <p>
61   * The owner can use <code>close</code> to gracefully shutdown the thread.
62   *
63   * @version     $Revision: 1.4 $ $Date: 2003/08/07 13:33:12 $
64   * @author      <a href="mailto:jima@exolab.org">Jim Alateras</a>
65   */
66  public class BlockingWorkerQueue
67      extends Thread {
68  
69      /***
70       * This is the runnable that will perform the work
71       */
72      private QueueWorker _worker = null;
73  
74      /***
75       * The list is used to queue work
76       */
77      private LinkedList _queue = new LinkedList();
78  
79      /***
80       * If this is set to true then we must close the worker queue
81       */
82      private boolean _closed = false;
83  
84  
85      /***
86       * Construct a blocking worker queue and attahc to the specified
87       * queue worker. Make the thread a deamon thread.
88       *
89       * @param name - the name of the thread
90       * @param worker - the queue worker attached to this queue
91       */
92      public BlockingWorkerQueue(String name, QueueWorker worker) {
93          super("BWQ:" + name);
94          _worker = worker;
95          this.setDaemon(true);
96      }
97  
98      /***
99       * Add some work to the end of the queue
100      *
101      * @param work - add this piece of work
102      */
103     public void add(Object object) {
104         synchronized (_queue) {
105             _queue.addLast(object);
106             _queue.notifyAll();
107         }
108     }
109 
110     /***
111      * This method is called once the thread has started. It basically loops
112      * forever removing work from the queue and passing it to the runnable.
113      * <p>
114      * Calling <code>close</code> on this object will terminate it.
115      */
116     public void run() {
117         while (!_closed) {
118             Object work = null;
119 
120             synchronized (_queue) {
121                 // if there are no messages in the queue then block
122                 if (_queue.size() == 0) {
123                     try {
124                         _queue.wait();
125                     } catch (InterruptedException exception) {
126                         // ignore the exception;
127                     }
128                     continue;
129                 }
130 
131                 // if we get this far then there is something in the queue.
132                 // Remove it and hand it to the worker
133                 work = _queue.removeFirst();
134             }
135 
136             if (work != null) {
137                 _worker.execute(work);
138             }
139         }
140     }
141 
142     /***
143      * Return the number of entries still on the queue
144      *
145      * @size int
146      */
147     public int size() {
148         return _queue.size();
149     }
150 
151     /***
152      * Close this worker queue
153      */
154     public void close() {
155         _closed = true;
156         interrupt();
157     }
158 
159 }
160