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


1 /*
2   File: LayeredSync.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
16 /**
17  * A class that can be used to compose Syncs.
18  * A LayeredSync object manages two other Sync objects,
19  * <em>outer</em> and <em>inner</em>. The acquire operation
20  * invokes <em>outer</em>.acquire() followed by <em>inner</em>.acquire(),
21  * but backing out of outer (via release) upon an exception in inner.
22  * The other methods work similarly.
23  * <p>
24  * LayeredSyncs can be used to compose arbitrary chains
25  * by arranging that either of the managed Syncs be another
26  * LayeredSync.
27  *
28  * <p>[<a HREF="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
29 **/
30
31
32 public class LayeredSync implements Sync {
33
34   protected final Sync outer_;
35   protected final Sync inner_;
36
37   /**
38    * Create a LayeredSync managing the given outer and inner Sync
39    * objects
40    **/
41
42   public LayeredSync(Sync outer, Sync inner) {
43     outer_ = outer;
44     inner_ = inner;
45   }
46
47   public void acquire() throws InterruptedException JavaDoc {
48     outer_.acquire();
49     try {
50       inner_.acquire();
51     }
52     catch (InterruptedException JavaDoc ex) {
53       outer_.release();
54       throw ex;
55     }
56   }
57
58   public boolean attempt(long msecs) throws InterruptedException JavaDoc {
59
60     long start = (msecs <= 0)? 0 : System.currentTimeMillis();
61     long waitTime = msecs;
62
63     if (outer_.attempt(waitTime)) {
64       try {
65         if (msecs > 0)
66           waitTime = msecs - (System.currentTimeMillis() - start);
67         if (inner_.attempt(waitTime))
68           return true;
69         else {
70           outer_.release();
71           return false;
72         }
73       }
74       catch (InterruptedException JavaDoc ex) {
75         outer_.release();
76         throw ex;
77       }
78     }
79     else
80       return false;
81   }
82
83   public void release() {
84     inner_.release();
85     outer_.release();
86   }
87
88 }
89
90
91
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