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Java > Open Source Codes > org > mr > core > util > SynchronizedQueue


1 /*
2  * Copyright 2002 by
3  * <a HREF="http://www.coridan.com">Coridan</a>
4  * <a HREF="mailto: support@coridan.com ">support@coridan.com</a>
5  *
6  * The contents of this file are subject to the Mozilla Public License Version
7  * 1.1 (the "License"); you may not use this file except in compliance with the
8  * License. You may obtain a copy of the License at
9  * http://www.mozilla.org/MPL/
10  *
11  * Software distributed under the License is distributed on an "AS IS" basis,
12  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
13  * for the specific language governing rights and limitations under the
14  * License.
15  *
16  * The Original Code is "MantaRay" (TM).
17  *
18  * The Initial Developer of the Original Code is Amir Shevat.
19  * Portions created by the Initial Developer are Copyright (C) 2006
20  * Coridan Inc. All Rights Reserved.
21  *
22  * Contributor(s): all the names of the contributors are added in the source
23  * code where applicable.
24  *
25  * Alternatively, the contents of this file may be used under the terms of the
26  * LGPL license (the "GNU LESSER GENERAL PUBLIC LICENSE"), in which case the
27  * provisions of LGPL are applicable instead of those above. If you wish to
28  * allow use of your version of this file only under the terms of the LGPL
29  * License and not to allow others to use your version of this file under
30  * the MPL, indicate your decision by deleting the provisions above and
31  * replace them with the notice and other provisions required by the LGPL.
32  * If you do not delete the provisions above, a recipient may use your version
33  * of this file under either the MPL or the GNU LESSER GENERAL PUBLIC LICENSE.
34  
35  *
36  * This library is free software; you can redistribute it and/or modify it
37  * under the terms of the MPL as stated above or under the terms of the GNU
38  * Lesser General Public License as published by the Free Software Foundation;
39  * either version 2.1 of the License, or any later version.
40  *
41  * This library is distributed in the hope that it will be useful, but WITHOUT
42  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
43  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
44  * License for more details.
45  */
46 package org.mr.core.util;
47
48 import java.util.LinkedList JavaDoc;
49 import java.util.List JavaDoc;
50
51 import org.apache.commons.logging.LogFactory;
52
53 /**
54  * A Queue is a FIFO (First In First Out) dispenser.
55  *
56  * @author Amir Shevat
57  * @version 1.0
58  */
59 public class SynchronizedQueue implements Queue {
60     protected List JavaDoc m_list;
61     
62
63     /**
64      * Default constructor
65      *
66      */
67     public SynchronizedQueue(){
68         m_list=new LinkedList JavaDoc();
69         
70     }
71
72     /**
73      * Enqueue an element into the queue
74      *
75      * @param o The element to enqueue
76      */
77     synchronized public boolean enqueue(Object JavaDoc o){
78        boolean b = m_list.add(o) ;
79       
80         notifyAll(); //Let waiting threads know that the queue is not empty.
81 return b;
82     }
83
84     /**
85      * De-queue an element from the queue
86      *
87      * @return The element
88      */
89     synchronized public Object JavaDoc dequeue() {
90         while(m_list.size() ==0) {
91             try {
92                 wait();
93             } catch (InterruptedException JavaDoc ex){
94                 if(LogFactory.getLog("SynchronizedQueue").isFatalEnabled())
95                     LogFactory.getLog("SynchronizedQueue").fatal("core Queue got at Exception" , ex);
96             }
97         }
98         return m_list.remove(0);
99     }
100     
101     /**
102      * De-queue an element from the queue or null if there is no element
103      *
104      * @return The element
105      */
106     synchronized public Object JavaDoc dequeueNoBlock(){
107         if(m_list.size() ==0)return null;
108         return m_list.remove(0);
109     }
110
111     /**
112      * De-queue an element from the queue. if no element, wait until element arrives,
113      * or timeout passed.
114      *
115      * @param timeout - millis to wait in case no message in queue
116      * @return - the element.
117      */
118     synchronized public Object JavaDoc dequeue(long timeout){
119         if(m_list.size() ==0) {
120             try {
121                 wait(timeout);
122             } catch (InterruptedException JavaDoc ex){
123                 if(LogFactory.getLog("SynchronizedQueue").isFatalEnabled())
124                     LogFactory.getLog("SynchronizedQueue").fatal("core Queue got at Exception" , ex);
125             }
126         }
127         return dequeueNoBlock();
128         
129     }
130     /**
131      * How many elements are currently enqueued?
132      *
133      * @return the number of elements in the queue
134      */
135      synchronized public int size() {
136         return m_list.size();
137      }
138
139
140     /**
141      * Is the queue empty?
142      *
143      * @return true iff the queue is empty
144      */
145     synchronized public boolean isEmpty(){
146         return (size()==0);
147     }
148
149     
150     
151     
152     /**
153      * clears the Q
154      *
155      */
156     public synchronized void clear(){
157         while(!isEmpty()){
158             this.dequeue();
159         }
160     }
161     
162     public List JavaDoc getUnderlineList(){
163         return m_list;
164     }
165
166 }
167
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