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annotate src/EDU/oswego/cs/dl/util/concurrent/PrioritySemaphore.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: 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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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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90 }