Mercurial > hg > blitz_condensed
annotate src/EDU/oswego/cs/dl/util/concurrent/FIFOSemaphore.java @ 34:6f68e94c1fb8 default tip
Add CondensedStats monitoring utility, equivalent to vmstat
author | Dominic Cleal <dominic-cleal@cdo2.com> |
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date | Thu, 05 Aug 2010 11:07:25 +0100 |
parents | 3dc0c5604566 |
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1 /* |
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2 File: FIFOSemaphore.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 First-in/First-out implementation of a Semaphore. |
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19 * Waiting requests will be satisified in |
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20 * the order that the processing of those requests got to a certain point. |
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21 * If this sounds vague it is meant to be. FIFO implies a |
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22 * logical timestamping at some point in the processing of the |
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23 * request. To simplify things we don't actually timestamp but |
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24 * simply store things in a FIFO queue. Thus the order in which |
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25 * requests enter the queue will be the order in which they come |
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26 * out. This order need not have any relationship to the order in |
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27 * which requests were made, nor the order in which requests |
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28 * actually return to the caller. These depend on Java thread |
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29 * scheduling which is not guaranteed to be predictable (although |
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30 * JVMs tend not to go out of their way to be unfair). |
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31 * <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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32 **/ |
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33 |
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34 public class FIFOSemaphore extends QueuedSemaphore { |
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35 |
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36 /** |
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37 * Create a Semaphore with the given initial number of permits. |
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38 * Using a seed of one makes the semaphore act as a mutual exclusion lock. |
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39 * Negative seeds are also allowed, in which case no acquires will proceed |
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40 * until the number of releases has pushed the number of permits past 0. |
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41 **/ |
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42 |
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43 public FIFOSemaphore(long initialPermits) { |
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44 super(new FIFOWaitQueue(), initialPermits); |
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45 } |
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46 |
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47 /** |
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48 * Simple linked list queue used in FIFOSemaphore. |
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49 * Methods are not synchronized; they depend on synch of callers |
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50 **/ |
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51 |
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52 protected static class FIFOWaitQueue extends WaitQueue { |
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53 protected WaitNode head_ = null; |
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54 protected WaitNode tail_ = null; |
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55 |
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56 protected void insert(WaitNode w) { |
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57 if (tail_ == null) |
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58 head_ = tail_ = w; |
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59 else { |
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60 tail_.next = w; |
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61 tail_ = w; |
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62 } |
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63 } |
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64 |
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65 protected WaitNode extract() { |
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66 if (head_ == null) |
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67 return null; |
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68 else { |
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69 WaitNode w = head_; |
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70 head_ = w.next; |
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71 if (head_ == null) tail_ = null; |
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72 w.next = null; |
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73 return w; |
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74 } |
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75 } |
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76 } |
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77 |
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78 } |