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annotate src/EDU/oswego/cs/dl/util/concurrent/ReadWriteLock.java @ 27:511648fa4d64 Version 2.1

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Version to 2.1
author Dan Creswell <dan.creswell@gmail.com>
date Mon, 04 Jan 2010 13:00:40 +0000
parents 3dc0c5604566
children
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1 /*
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2 File: ReadWriteLock.java
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3
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4 Originally written by Doug Lea and released into the public domain.
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5 This may be used for any purposes whatsoever without acknowledgment.
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6 Thanks for the assistance and support of Sun Microsystems Labs,
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7 and everyone contributing, testing, and using this code.
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8
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9 History:
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10 Date Who What
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11 11Jun1998 dl Create public version
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12 */
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15 package EDU.oswego.cs.dl.util.concurrent;
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18 /**
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19 * ReadWriteLocks maintain a pair of associated locks.
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20 * The readLock may be held simultanously by multiple
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21 * reader threads, so long as there are no writers. The writeLock
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22 * is exclusive. ReadWrite locks are generally preferable to
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23 * plain Sync locks or synchronized methods in cases where:
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24 * <ul>
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25 * <li> The methods in a class can be cleanly separated into
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26 * those that only access (read) data vs those that
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27 * modify (write).
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28 * <li> Target applications generally have more readers than writers.
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29 * <li> The methods are relatively time-consuming (as a rough
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30 * rule of thumb, exceed more than a hundred instructions), so it
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31 * pays to introduce a bit more overhead associated with
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32 * ReadWrite locks compared to simple synchronized methods etc
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33 * in order to allow concurrency among reader threads.
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34 *
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35 * </ul>
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36 * Different implementation classes differ in policies surrounding
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37 * which threads to prefer when there is
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38 * contention. By far, the most commonly useful policy is
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39 * WriterPreferenceReadWriteLock. The other implementations
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40 * are targeted for less common, niche applications.
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41 *<p>
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42 * Standard usage:
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43 * <pre>
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44 * class X {
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45 * ReadWriteLock rw;
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46 * // ...
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47 *
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48 * public void read() throws InterruptedException {
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49 * rw.readLock().acquire();
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50 * try {
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51 * // ... do the read
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52 * }
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53 * finally {
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54 * rw.readlock().release()
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55 * }
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56 * }
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57 *
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58 *
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59 * public void write() throws InterruptedException {
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60 * rw.writeLock().acquire();
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61 * try {
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62 * // ... do the write
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63 * }
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64 * finally {
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65 * rw.writelock().release()
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66 * }
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67 * }
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68 * }
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69 * </pre>
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70 * @see Sync
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71 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
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72
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73 **/
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74
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75 public interface ReadWriteLock {
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76 /** get the readLock **/
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77 Sync readLock();
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78
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79 /** get the writeLock **/
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80 Sync writeLock();
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81 }
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