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25 
26 package java.nio.channels.spi;
27 
28 import java.nio.channels.*;
29 
30 
31 /**
32  * Base implementation class for selection keys.
33  *
34  * <p> This class tracks the validity of the key and implements cancellation.
35  *
36  * @author Mark Reinhold
37  * @author JSR-51 Expert Group
38  * @since 1.4
39  */
40 
41 public abstract class AbstractSelectionKey
42     extends SelectionKey
43 {
44 
45     /**
46      * Initializes a new instance of this class.
47      */
AbstractSelectionKey()48     protected AbstractSelectionKey() { }
49 
50     private volatile boolean valid = true;
51 
isValid()52     public final boolean isValid() {
53         return valid;
54     }
55 
invalidate()56     void invalidate() {                                 // package-private
57         valid = false;
58     }
59 
60     /**
61      * Cancels this key.
62      *
63      * <p> If this key has not yet been cancelled then it is added to its
64      * selector's cancelled-key set while synchronized on that set.  </p>
65      */
cancel()66     public final void cancel() {
67         // Synchronizing "this" to prevent this key from getting canceled
68         // multiple times by different threads, which might cause race
69         // condition between selector's select() and channel's close().
70         synchronized (this) {
71             if (valid) {
72                 valid = false;
73                 ((AbstractSelector)selector()).cancel(this);
74             }
75         }
76     }
77 }
78