Slot


1   /*
2     File: Slot.java
3   
4     Originally written by Doug Lea and released into the public domain.
5     This may be used for any purposes whatsoever without acknowledgment.
6     Thanks for the assistance and support of Sun Microsystems Labs,
7     and everyone contributing, testing, and using this code.
8   
9     History:
10    Date       Who                What
11    11Jun1998  dl               Create public version
12    25aug1998  dl               added peek
13  */
14  
15  package EDU.oswego.cs.dl.util.concurrent;
16  import java.lang.reflect.*;
17  
18  /**
19   * A one-slot buffer, using semaphores to control access.
20   * Slots are usually more efficient and controllable than using other
21   * bounded buffers implementations with capacity of 1.
22   * <p>
23   * Among other applications, Slots can be convenient in token-passing
24   * designs: Here. the Slot holds a some object serving as a token,
25   * that can be obtained
26   * and returned by various threads.
27   *
28   * <p>[<a HREF="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
29  **/
30  
31  public class Slot extends SemaphoreControlledChannel {
32  
33    /**
34     * Create a buffer with the given capacity, using
35     * the supplied Semaphore class for semaphores.
36     * @exception NoSuchMethodException If class does not have constructor 
37     * that intializes permits
38     * @exception SecurityException if constructor information 
39     * not accessible
40     * @exception InstantiationException if semaphore class is abstract
41     * @exception IllegalAccessException if constructor cannot be called
42     * @exception InvocationTargetException if semaphore constructor throws an
43     * exception
44     **/
45  
46    public Slot(Class   semaphoreClass) 
47     throws NoSuchMethodException  , 
48            SecurityException  , 
49            InstantiationException  , 
50            IllegalAccessException  , 
51            InvocationTargetException {
52      super(1, semaphoreClass);
53    }
54  
55    /** 
56     * Create a new Slot using default Semaphore implementations 
57     **/
58    public Slot() {
59      super(1);
60    }
61  
62    /** The slot **/
63    protected Object   item_ = null;
64  
65  
66    /** Set the item in preparation for a take **/
67    protected synchronized void insert(Object   x) { 
68      item_ = x; 
69    }
70  
71    /** Take item known to exist **/
72    protected synchronized Object   extract() { 
73      Object   x = item_;
74      item_ = null;
75      return x;
76    }
77  
78    public synchronized Object   peek() {
79      return item_;
80    }
81  
82  }
83
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