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Code - Class EDU.oswego.cs.dl.util.concurrent.ReadWriteLock

1 /*
2   File: ReadWriteLock.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   11Jun1998 dl Create public version
12 */
13
14
15 package EDU.oswego.cs.dl.util.concurrent;
16
17
18 /**
19 * ReadWriteLocks maintain a pair of associated locks.
20 * The readLock may be held simultanously by multiple
21 * reader threads, so long as there are no writers. The writeLock
22 * is exclusive. ReadWrite locks are generally preferable to
23 * plain Sync locks or synchronized methods in cases where:
24 * <ul>
25 * <li> The methods in a class can be cleanly separated into
26 * those that only access (read) data vs those that
27 * modify (write).
28 * <li> Target applications generally have more readers than writers.
29 * <li> The methods are relatively time-consuming (as a rough
30 * rule of thumb, exceed more than a hundred instructions), so it
31 * pays to introduce a bit more overhead associated with
32 * ReadWrite locks compared to simple synchronized methods etc
33 * in order to allow concurrency among reader threads.
34 *
35 * </ul>
36 * Different implementation classes differ in policies surrounding
37 * which threads to prefer when there is
38 * contention. By far, the most commonly useful policy is
39 * WriterPreferenceReadWriteLock. The other implementations
40 * are targeted for less common, niche applications.
41 *<p>
42 * Standard usage:
43 * <pre>
44 * class X {
45 * ReadWriteLock rw;
46 * // ...
47 *
48 * public void read() throws InterruptedException {
49 * rw.readLock().acquire();
50 * try {
51 * // ... do the read
52 * }
53 * finally {
54 * rw.readlock().release()
55 * }
56 * }
57 *
58 *
59 * public void write() throws InterruptedException {
60 * rw.writeLock().acquire();
61 * try {
62 * // ... do the write
63 * }
64 * finally {
65 * rw.writelock().release()
66 * }
67 * }
68 * }
69 * </pre>
70 * @see Sync
71 * <p>[<a HREF="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
72
73 **/
74
75 public interface ReadWriteLock {
76   /** get the readLock **/
77   Sync readLock();
78
79   /** get the writeLock **/
80   Sync writeLock();
81 }
82
83