Mercurial > hg > blitz_condensed
annotate src/EDU/oswego/cs/dl/util/concurrent/Latch.java @ 28:4b2f23b6feca
Add a schema compatibility check to indexer that parallels storage.
author | Dan Creswell <dan.creswell@gmail.com> |
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date | Sat, 12 Jun 2010 10:11:15 +0100 |
parents | 3dc0c5604566 |
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1 /* |
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2 File: Latch.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 package EDU.oswego.cs.dl.util.concurrent; |
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15 |
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16 /** |
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17 * A latch is a boolean condition that is set at most once, ever. |
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18 * Once a single release is issued, all acquires will pass. |
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19 * <p> |
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20 * <b>Sample usage.</b> Here are a set of classes that use |
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21 * a latch as a start signal for a group of worker threads that |
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22 * are created and started beforehand, and then later enabled. |
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23 * <pre> |
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24 * class Worker implements Runnable { |
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25 * private final Latch startSignal; |
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26 * Worker(Latch l) { startSignal = l; } |
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27 * public void run() { |
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28 * startSignal.acquire(); |
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29 * doWork(); |
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30 * } |
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31 * void doWork() { ... } |
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32 * } |
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33 * |
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34 * class Driver { // ... |
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35 * void main() { |
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36 * Latch go = new Latch(); |
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37 * for (int i = 0; i < N; ++i) // make threads |
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38 * new Thread(new Worker(go)).start(); |
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39 * doSomethingElse(); // don't let run yet |
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40 * go.release(); // let all threads proceed |
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41 * } |
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42 * } |
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43 *</pre> |
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44 * [<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p> |
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45 **/ |
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46 |
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47 public class Latch implements Sync { |
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48 protected boolean latched_ = false; |
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49 |
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50 /* |
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51 This could use double-check, but doesn't. |
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52 If the latch is being used as an indicator of |
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53 the presence or state of an object, the user would |
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54 not necessarily get the memory barrier that comes with synch |
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55 that would be needed to correctly use that object. This |
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56 would lead to errors that users would be very hard to track down. So, to |
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57 be conservative, we always use synch. |
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58 */ |
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59 |
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60 public void acquire() throws InterruptedException { |
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61 if (Thread.interrupted()) throw new InterruptedException(); |
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62 synchronized(this) { |
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63 while (!latched_) |
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64 wait(); |
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65 } |
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66 } |
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67 |
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68 public boolean attempt(long msecs) throws InterruptedException { |
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69 if (Thread.interrupted()) throw new InterruptedException(); |
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70 synchronized(this) { |
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71 if (latched_) |
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72 return true; |
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73 else if (msecs <= 0) |
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74 return false; |
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75 else { |
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76 long waitTime = msecs; |
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77 long start = System.currentTimeMillis(); |
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78 for (;;) { |
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79 wait(waitTime); |
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80 if (latched_) |
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81 return true; |
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82 else { |
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83 waitTime = msecs - (System.currentTimeMillis() - start); |
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84 if (waitTime <= 0) |
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85 return false; |
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86 } |
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87 } |
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88 } |
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89 } |
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90 } |
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91 |
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92 /** Enable all current and future acquires to pass **/ |
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93 public synchronized void release() { |
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94 latched_ = true; |
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95 notifyAll(); |
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96 } |
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97 |
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98 } |
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99 |