Mercurial > hg > blitz_stable
annotate src/EDU/oswego/cs/dl/util/concurrent/PrioritySemaphore.java @ 27:511648fa4d64 Version 2.1
Version to 2.1
author | Dan Creswell <dan.creswell@gmail.com> |
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date | Mon, 04 Jan 2010 13:00:40 +0000 |
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1 /* |
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2 File: PrioritySemaphore.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 * A Semaphore that grants requests to threads with higher |
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19 * Thread priority rather than lower priority when there is |
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20 * contention. Ordering of requests with the same priority |
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21 * is approximately FIFO. |
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22 * Priorities are based on Thread.getPriority. |
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23 * Changing the priority of an already-waiting thread does NOT |
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24 * change its ordering. This class also does not specially deal with priority |
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25 * inversion -- when a new high-priority thread enters |
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26 * while a low-priority thread is currently running, their |
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27 * priorities are <em>not</em> artificially manipulated. |
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28 * <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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29 |
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30 **/ |
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31 |
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32 public class PrioritySemaphore extends QueuedSemaphore { |
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33 |
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34 /** |
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35 * Create a Semaphore with the given initial number of permits. |
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36 * Using a seed of one makes the semaphore act as a mutual exclusion lock. |
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37 * Negative seeds are also allowed, in which case no acquires will proceed |
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38 * until the number of releases has pushed the number of permits past 0. |
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39 **/ |
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40 |
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41 |
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42 public PrioritySemaphore(long initialPermits) { |
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43 super(new PriorityWaitQueue(), initialPermits); |
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44 } |
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45 |
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46 protected static class PriorityWaitQueue extends WaitQueue { |
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47 |
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48 |
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49 /** An array of wait queues, one per priority **/ |
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50 protected final FIFOSemaphore.FIFOWaitQueue[] cells_ = |
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51 new FIFOSemaphore.FIFOWaitQueue[Thread.MAX_PRIORITY - |
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52 Thread.MIN_PRIORITY + 1]; |
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53 |
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54 /** |
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55 * The index of the highest priority cell that may need to be signalled, |
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56 * or -1 if none. Used to minimize array traversal. |
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57 **/ |
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58 |
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59 protected int maxIndex_ = -1; |
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60 |
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61 protected PriorityWaitQueue() { |
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62 for (int i = 0; i < cells_.length; ++i) |
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63 cells_[i] = new FIFOSemaphore.FIFOWaitQueue(); |
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64 } |
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65 |
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66 protected void insert(WaitNode w) { |
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67 int idx = Thread.currentThread().getPriority() - Thread.MIN_PRIORITY; |
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68 cells_[idx].insert(w); |
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69 if (idx > maxIndex_) maxIndex_ = idx; |
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70 } |
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71 |
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72 protected WaitNode extract() { |
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73 for (;;) { |
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74 int idx = maxIndex_; |
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75 if (idx < 0) |
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76 return null; |
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77 WaitNode w = cells_[idx].extract(); |
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78 if (w != null) |
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79 return w; |
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80 else |
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81 --maxIndex_; |
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82 } |
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83 } |
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84 } |
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85 |
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90 } |