/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * particular file as subject to the "Classpath" exception as provided

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 */

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);

            }

        }

    }

}