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Java > Open Source Codes > org > apache > avalon > excalibur > concurrent > ConditionalEvent


1 /*
2
3  ============================================================================
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5  ============================================================================
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7  Copyright (C) 1999-2003 The Apache Software Foundation. All rights reserved.
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9  Redistribution and use in source and binary forms, with or without modifica-
10  tion, are permitted provided that the following conditions are met:
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13     this list of conditions and the following disclaimer.
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25  4. The names "Jakarta", "Avalon", "Excalibur" and "Apache Software Foundation"
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49 */
50 package org.apache.avalon.excalibur.concurrent;
51
52 /**
53  * This class implements a POSIX style "Event" object. The difference
54  * between the ConditionalEvent and the java wait()/notify() technique is in
55  * handling of event state. If a ConditionalEvent is signalled, a thread
56  * that subsequently waits on it is immediately released. In case of auto
57  * reset EventObjects, the object resets (unsignalled) itself as soon as it
58  * is signalled and waiting thread(s) are released (based on whether signal()
59  * or signalAll() was called).
60  *
61  * @deprecated use EDU.oswego.cs.dl.util.concurrent.CondVar instead
62  *
63  * @author <a HREF="mailto:kranga@sapient.com">Karthik Rangaraju</a>
64  * @version CVS $Revision: 1.4 $ $Date: 2003/03/22 12:46:23 $
65  * @since 4.0
66  */
67 public class ConditionalEvent
68 {
69     private boolean m_state = false;
70     private boolean m_autoReset = false;
71
72     // TODO: Need to add methods that block until a specified time and
73 // return (though in real-life, I've never known what to do if a thread
74 // timesout other than call the method again)!
75
76     /**
77      * Creates a manual reset ConditionalEvent with a specified initial state
78      *
79      * @param initialState Sets the initial state of the ConditionalEvent.
80      * Signalled if pInitialState is true, unsignalled otherwise.
81      */
82     public ConditionalEvent( boolean initialState )
83     {
84         m_state = initialState;
85     }
86
87     /**
88      * Creates a ConditionalEvent with the defined initial state.
89      *
90      * @param initialState if true, the ConditionalEvent is signalled when
91      * created.
92      * @param autoReset if true creates an auto-reset ConditionalEvent
93      */
94     public ConditionalEvent( boolean initialState, boolean autoReset )
95     {
96         m_state = initialState;
97         m_autoReset = autoReset;
98     }
99
100     /**
101      * Checks if the event is signalled. Does not block on the operation.
102      *
103      * @return true is event is signalled, false otherwise. Does not reset
104      * an autoreset event
105      */
106     public boolean isSignalled()
107     {
108         return m_state;
109     }
110
111     /**
112      * Signals the event. A single thread blocked on waitForSignal() is released.
113      *
114      * @see #signalAll()
115      * @see #waitForSignal()
116      */
117     public void signal()
118     {
119         synchronized( this )
120         {
121             m_state = true;
122             notify();
123         }
124     }
125
126     /**
127      * Current implementation only works with manual reset events. Releases.
128      *
129      * all threads blocked on waitForSignal()
130      * @see #waitForSignal()
131      */
132     public void signalAll()
133     {
134         synchronized( this )
135         {
136             m_state = true;
137             notifyAll();
138         }
139     }
140
141     /**
142      * Resets the event to an unsignalled state
143      */
144     public void reset()
145     {
146         synchronized( this )
147         {
148             m_state = false;
149         }
150     }
151
152     /**
153      * If the event is signalled, this method returns immediately resetting the
154      * signal, otherwise it blocks until the event is signalled.
155      *
156      * @throws InterruptedException if the thread is interrupted when blocked
157      */
158     public void waitForSignal()
159         throws InterruptedException JavaDoc
160     {
161         synchronized( this )
162         {
163             while( !m_state )
164             {
165                 wait();
166             }
167             if( m_autoReset )
168             {
169                 m_state = false;
170             }
171         }
172     }
173 }
174
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