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 * Copyright (c) 2000, 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.nio.channels.spi;

import java.nio.channels.*;


/**
 * Base implementation class for selection keys.
 *
 * <p> This class tracks the validity of the key and implements cancellation.
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public abstract class AbstractSelectionKey
    extends SelectionKey
{

    /**
     * Initializes a new instance of this class.  </p>
     */
    protected AbstractSelectionKey() { }

    private volatile boolean valid = true;

    public final boolean isValid() {
        return valid;
    }

    void invalidate() {                                 // package-private
        valid = false;
    }

    /**
     * Cancels this key.
     *
     * <p> If this key has not yet been cancelled then it is added to its
     * selector's cancelled-key set while synchronized on that set.  </p>
     */
    public final void cancel() {
        // Synchronizing "this" to prevent this key from getting canceled
        // multiple times by different threads, which might cause race
        // condition between selector's select() and channel's close().
        synchronized (this) {
            if (valid) {
                valid = false;
                ((AbstractSelector)selector()).cancel(this);
            }
        }
    }
}