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annotate src/EDU/oswego/cs/dl/util/concurrent/Slot.java @ 18:4580bb12db30

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Separate command execution from command logging.
author Dan Creswell <dan.creswell@gmail.com>
date Sun, 05 Jul 2009 16:26:25 +0100
parents 3dc0c5604566
children
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1 /*
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2 File: Slot.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 25aug1998 dl added peek
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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 import java.lang.reflect.*;
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17
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18 /**
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19 * A one-slot buffer, using semaphores to control access.
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20 * Slots are usually more efficient and controllable than using other
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21 * bounded buffers implementations with capacity of 1.
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22 * <p>
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23 * Among other applications, Slots can be convenient in token-passing
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24 * designs: Here. the Slot holds a some object serving as a token,
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25 * that can be obtained
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26 * and returned by various threads.
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27 *
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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 public class Slot extends SemaphoreControlledChannel {
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32
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33 /**
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34 * Create a buffer with the given capacity, using
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35 * the supplied Semaphore class for semaphores.
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36 * @exception NoSuchMethodException If class does not have constructor
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37 * that intializes permits
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38 * @exception SecurityException if constructor information
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39 * not accessible
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40 * @exception InstantiationException if semaphore class is abstract
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41 * @exception IllegalAccessException if constructor cannot be called
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42 * @exception InvocationTargetException if semaphore constructor throws an
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43 * exception
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44 **/
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45
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46 public Slot(Class semaphoreClass)
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47 throws NoSuchMethodException,
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48 SecurityException,
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49 InstantiationException,
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50 IllegalAccessException,
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51 InvocationTargetException {
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52 super(1, semaphoreClass);
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53 }
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54
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55 /**
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56 * Create a new Slot using default Semaphore implementations
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57 **/
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58 public Slot() {
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59 super(1);
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60 }
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61
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62 /** The slot **/
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63 protected Object item_ = null;
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64
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65
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66 /** Set the item in preparation for a take **/
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67 protected synchronized void insert(Object x) {
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68 item_ = x;
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69 }
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70
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71 /** Take item known to exist **/
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72 protected synchronized Object extract() {
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73 Object x = item_;
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74 item_ = null;
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75 return x;
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76 }
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77
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78 public synchronized Object peek() {
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79 return item_;
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80 }
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81
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82 }