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Java > Open Source Codes > com > caucho > make > CachedDependency


1 /*
2  * Copyright (c) 1998-2006 Caucho Technology -- all rights reserved
3  *
4  * This file is part of Resin(R) Open Source
5  *
6  * Each copy or derived work must preserve the copyright notice and this
7  * notice unmodified.
8  *
9  * Resin Open Source is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU General Public License as published by
11  * the Free Software Foundation; either version 2 of the License, or
12  * (at your option) any later version.
13  *
14  * Resin Open Source is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
17  * of NON-INFRINGEMENT. See the GNU General Public License for more
18  * details.
19  *
20  * You should have received a copy of the GNU General Public License
21  * along with Resin Open Source; if not, write to the
22  *
23  * Free Software Foundation, Inc.
24  * 59 Temple Place, Suite 330
25  * Boston, MA 02111-1307 USA
26  *
27  * @author Scott Ferguson
28  */
29
30 package com.caucho.make;
31
32 import com.caucho.loader.Environment;
33 import com.caucho.util.Alarm;
34 import com.caucho.vfs.Dependency;
35
36 /**
37  * A cached dependency only checks the dependency at an interval.
38  */
39 abstract public class CachedDependency implements Dependency {
40   private long _checkInterval;
41   private long _lastCheckTime;
42   private boolean _isModified;
43
44   public CachedDependency()
45   {
46     _checkInterval = Environment.getDependencyCheckInterval();
47   }
48   
49   /**
50    * Gets the check interval.
51    */
52   public long getCheckInterval()
53   {
54     return _checkInterval;
55   }
56
57   /**
58    * Gets the check interval.
59    */
60   public void setCheckInterval(long checkInterval)
61   {
62     _checkInterval = checkInterval;
63   }
64   
65   /**
66    * Returns true if the underlying resource has changed.
67    */
68   public final boolean isModified()
69   {
70     long now = Alarm.getCurrentTime();
71     if (now <= _lastCheckTime + _checkInterval)
72       return _isModified;
73     
74     synchronized (this) {
75       now = Alarm.getCurrentTime();
76       
77       if (now <= _lastCheckTime + _checkInterval)
78     return _isModified;
79
80       _lastCheckTime = now;
81     }
82
83     _isModified = isModifiedImpl();
84
85     return _isModified;
86   }
87   
88   /**
89    * Returns true if the underlying resource has changed.
90    */
91   abstract public boolean isModifiedImpl();
92 }
93
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