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Java > Open Source Codes > org > apache > avalon > excalibur > monitor > impl > ActiveMonitor


1 /*
2
3  ============================================================================
4                    The Apache Software License, Version 1.1
5  ============================================================================
6  
7  Copyright (C) 1999-2003 The Apache Software Foundation. All rights reserved.
8  
9  Redistribution and use in source and binary forms, with or without modifica-
10  tion, are permitted provided that the following conditions are met:
11  
12  1. Redistributions of source code must retain the above copyright notice,
13     this list of conditions and the following disclaimer.
14  
15  2. Redistributions in binary form must reproduce the above copyright notice,
16     this list of conditions and the following disclaimer in the documentation
17     and/or other materials provided with the distribution.
18  
19  3. The end-user documentation included with the redistribution, if any, must
20     include the following acknowledgment: "This product includes software
21     developed by the Apache Software Foundation (http://www.apache.org/)."
22     Alternately, this acknowledgment may appear in the software itself, if
23     and wherever such third-party acknowledgments normally appear.
24  
25  4. The names "Jakarta", "Avalon", "Excalibur" and "Apache Software Foundation"
26     must not be used to endorse or promote products derived from this software
27     without prior written permission. For written permission, please contact
28     apache@apache.org.
29  
30  5. Products derived from this software may not be called "Apache", nor may
31     "Apache" appear in their name, without prior written permission of the
32     Apache Software Foundation.
33  
34  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
35  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
36  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
37  APACHE SOFTWARE FOUNDATION OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
38  INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLU-
39  DING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
40  OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
41  ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
42  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
43  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
44  
45  This software consists of voluntary contributions made by many individuals
46  on behalf of the Apache Software Foundation. For more information on the
47  Apache Software Foundation, please see <http://www.apache.org/>.
48  
49 */
50 package org.apache.avalon.excalibur.monitor.impl;
51
52 /**
53  * The ActiveMonitor is used to actively check a set of resources to see if they have
54  * changed. It will poll the resources with a frequency as specified or if
55  * unspecified with the default (60 seconds).
56  *
57  * @author <a HREF="mailto:bloritsch@apache.org">Berin Loritsch</a>
58  * @author <a HREF="mailto:peter at apache.org">Peter Donald</a>
59  * @version $Id: ActiveMonitor.java,v 1.9 2003/05/23 17:41:04 bloritsch Exp $
60  */
61 public class ActiveMonitor
62     extends AbstractMonitor
63     implements Runnable JavaDoc
64 {
65     private static final long DEFAULT_FREQUENCY = 1000L * 60L;
66
67     /**
68      * The frequency to scan resources for changes measured
69      * in milliseconds.
70      */
71     private long m_frequency = DEFAULT_FREQUENCY;
72
73     /**
74      * The priority of the thread that monitors resources. Defaults
75      * to System specific {@link Thread#MIN_PRIORITY}.
76      */
77     private int m_priority = Thread.MIN_PRIORITY;
78
79     /**
80      * The thread that does the monitoring.
81      */
82     private final Thread JavaDoc m_monitorThread = new Thread JavaDoc( this );
83
84     /**
85      * Set to false to shutdown the thread.
86      */
87     private volatile boolean m_keepRunning = true;
88
89     /**
90      * Set the frequency with which the monitor
91      * checks the resources. This can be changed
92      * anytime and will be enabled the next time
93      * through the check.
94      *
95      * @param frequency the frequency to scan resources for changes
96      */
97     public void setFrequency( final long frequency )
98     {
99         m_frequency = frequency;
100     }
101
102     /**
103      * Set the priority of the active monitors thread.
104      *
105      * @param priority the priority of the active monitors thread.
106      */
107     public void setPriority( final int priority )
108     {
109         m_priority = priority;
110     }
111
112     public void start()
113         throws Exception JavaDoc
114     {
115         m_keepRunning = true;
116         m_monitorThread.setDaemon( true );
117         m_monitorThread.setPriority( m_priority );
118         m_monitorThread.start();
119     }
120
121     public void stop()
122         throws Exception JavaDoc
123     {
124         m_keepRunning = false;
125         m_monitorThread.interrupt();
126         m_monitorThread.join();
127     }
128
129     public final void run()
130     {
131         try
132         {
133             while( m_keepRunning )
134             {
135                 Thread.sleep( m_frequency );
136                 scanAllResources();
137             }
138         }
139         catch( InterruptedException JavaDoc e )
140         {
141             // clears the interrupted status
142 Thread.interrupted();
143         }
144     }
145 }
146
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