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Java > Open Source Codes > org > exolab > jms > util > BlockingWorkerQueue


1 /**
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21  * nor may "Exolab" appear in their names without prior written
22  * permission of Exoffice Technologies. Exolab is a registered
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26  * (http://www.exolab.org/).
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28  * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29  * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
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37  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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39  * OF THE POSSIBILITY OF SUCH DAMAGE.
40  *
41  * Copyright 2000 (C) Exoffice Technologies Inc. All Rights Reserved.
42  *
43  * $Id: BlockingWorkerQueue.java,v 1.1 2004/11/26 01:51:02 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 JavaDoc;
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: 1.1 $ $Date: 2004/11/26 01:51:02 $
64  * @author <a HREF="mailto:jima@exolab.org">Jim Alateras</a>
65  */
66 public class BlockingWorkerQueue
67     extends Thread JavaDoc {
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 JavaDoc _queue = new LinkedList JavaDoc();
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 JavaDoc 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 JavaDoc 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 JavaDoc 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 JavaDoc 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
161
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