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Java > Open Source Codes > EDU > oswego > cs > dl > util > concurrent > ObservableSync


1 /*
2   File: ObservableSync.java
3
4   Originally written by Doug Lea and released into the public domain.
5   This may be used for any purposes whatsoever without acknowledgment.
6   Thanks for the assistance and support of Sun Microsystems Labs,
7   and everyone contributing, testing, and using this code.
8
9   History:
10   Date Who What
11   1Aug1998 dl Create public version
12 */
13
14 package EDU.oswego.cs.dl.util.concurrent;
15 import java.util.*;
16
17 /**
18  * The ObservableSync class performs no synchronization
19  * itself, but invokes event-style messages to other
20  * observer objects upon invocation of Sync methods.
21  * These observers typically perform monitoring, logging,
22  * or other bookkeeping operations surrounding the object
23  * being managed by this Sync object.
24  * <p>
25  * Because ObservableSync does not itself perform any synchronization
26  * control, the attempt operation always succeeds.
27  * This class is typically used (via LayeredSync) as a wrapper
28  * around those that do perform synchronization control.
29  * <p>
30  * This class is based around a standard Observer design pattern.
31  * It is not hard to convert this to instead use a Listener
32  * design (as seen in AWT and JavaBeans), by defining associated
33  * EventObjects and forwarding them.
34  * <p>[<a HREF="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
35  * @see LayeredSync
36 **/
37
38
39 public class ObservableSync implements Sync {
40
41
42   /**
43    * Interface for objects that observe ObservableSyncs.
44    **/
45   public interface SyncObserver {
46     /**
47      * Method called upon acquire or successful attempt of Sync
48      **/
49
50     public void onAcquire(Object JavaDoc arg);
51
52     /**
53      * Method called upon release of Sync.
54      **/
55     public void onRelease(Object JavaDoc arg);
56   }
57
58   protected final CopyOnWriteArraySet observers_ = new CopyOnWriteArraySet();
59   protected Object JavaDoc arg_;
60
61   /**
62    * Create an ObservableSync that uses the supplied argument
63    * for all notifications. The argument is typically an
64    * object that is being managed by this Sync object.
65    **/
66
67   public ObservableSync(Object JavaDoc notificationArgument) {
68     arg_ = notificationArgument;
69   }
70
71   /**
72    * Return the argument used for notifications
73    **/
74   public synchronized Object JavaDoc getNotificationArgument() {
75     return arg_;
76   }
77
78   /**
79    * Set the argument used for notifications.
80    * @return the previous value of this argument
81    **/
82
83   public synchronized Object JavaDoc setNotificationArgument(Object JavaDoc notificationArg) {
84     Object JavaDoc old = arg_;
85     arg_ = notificationArg;
86     return old;
87   }
88
89
90
91   public void acquire() {
92     Object JavaDoc arg = getNotificationArgument();
93     for (Iterator it = observers_.iterator(); it.hasNext(); ) {
94       ((SyncObserver)it.next()).onAcquire(arg);
95     }
96   }
97
98   public boolean attempt(long msecs) {
99     acquire();
100     return true;
101   }
102
103   public void release() {
104     Object JavaDoc arg = getNotificationArgument();
105     for (Iterator it = observers_.iterator(); it.hasNext(); ) {
106       ((SyncObserver)it.next()).onRelease(arg);
107     }
108   }
109
110
111
112   /** Add obs to the set of observers **/
113   public void attach(SyncObserver obs) {
114     observers_.add(obs);
115   }
116
117   /** Remove obs from the set of observers. No effect if not in set **/
118   public void detach(SyncObserver obs) {
119     observers_.remove(obs);
120   }
121
122   /** Return an iterator that can be used to traverse through
123    * current set of observers
124    **/
125
126   public Iterator observers() {
127     return observers_.iterator();
128   }
129
130
131 }
132
133
134
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