Mercurial > hg > blitz_stable
annotate src/EDU/oswego/cs/dl/util/concurrent/ReadWriteLock.java @ 8:fa7203ea1622
Remove some dead code (Dave Brosius)
author | Dan Creswell <dan.creswell@gmail.com> |
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date | Sat, 23 May 2009 11:27:41 +0100 |
parents | 3dc0c5604566 |
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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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13 |
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14 |
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15 package EDU.oswego.cs.dl.util.concurrent; |
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16 |
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17 |
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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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82 |