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 * accompanied this code).

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package java.nio.channels.spi;

import java.io.IOException;

import java.nio.channels.SelectionKey;

import java.nio.channels.Selector;

import java.util.HashSet;

import java.util.Set;

import sun.nio.ch.Interruptible;

/**

 * Base implementation class for selectors.

 *

 * <p> This class encapsulates the low-level machinery required to implement

 * the interruption of selection operations.  A concrete selector class must

 * invoke the {@link #begin begin} and {@link #end end} methods before and

 * after, respectively, invoking an I/O operation that might block

 * indefinitely.  In order to ensure that the {@link #end end} method is always

 * invoked, these methods should be used within a

 * {@code try} ... {@code finally} block:

 *

 * <blockquote><pre id="be">

 * try {

 *     begin();

 *     // Perform blocking I/O operation here

 *     ...

 * } finally {

 *     end();

 * }</pre></blockquote>

 *

 * <p> This class also defines methods for maintaining a selector's

 * cancelled-key set and for removing a key from its channel's key set, and

 * declares the abstract {@link #register register} method that is invoked by a

 * selectable channel's {@link AbstractSelectableChannel#register register}

 * method in order to perform the actual work of registering a channel.  </p>

 *

 *

 * @author Mark Reinhold

 * @author JSR-51 Expert Group

 * @since 1.4

 */

public abstract class AbstractSelector

    extends Selector

{

    // The provider that created this selector

    private final SelectorProvider provider;

    /**

     * Initializes a new instance of this class.

     *

     * @param  provider

     *         The provider that created this selector

     */

    protected AbstractSelector(SelectorProvider provider) {

        this.provider = provider;

    }

    void cancel(SelectionKey k) {                       // package-private

        synchronized (cancelledKeys) {

            cancelledKeys.add(k);

        }

    }

    /**

     * Closes this selector.

     *

     * <p> If the selector has already been closed then this method returns

     * immediately.  Otherwise it marks the selector as closed and then invokes

     * the {@link #implCloseSelector implCloseSelector} method in order to

     * complete the close operation.  </p>

     *

     * @throws  IOException

     *          If an I/O error occurs

     */

    public final void close() throws IOException {

    }

    /**

     * Closes this selector.

     *

     * <p> This method is invoked by the {@link #close close} method in order

     * to perform the actual work of closing the selector.  This method is only

     * invoked if the selector has not yet been closed, and it is never invoked

     * more than once.

     *

     * <p> An implementation of this method must arrange for any other thread

     * that is blocked in a selection operation upon this selector to return

     * immediately as if by invoking the {@link

     * java.nio.channels.Selector#wakeup wakeup} method. </p>

     *

     * @throws  IOException

     *          If an I/O error occurs while closing the selector

     */

    protected abstract void implCloseSelector() throws IOException;

    public final boolean isOpen() {

    }

    /**

     * Returns the provider that created this channel.

     *

     * @return  The provider that created this channel

     */

    public final SelectorProvider provider() {

        return provider;

    }

    /**

     * Retrieves this selector's cancelled-key set.

     *

     * <p> This set should only be used while synchronized upon it.  </p>

     *

     * @return  The cancelled-key set

     */

    protected final Set<SelectionKey> cancelledKeys() {

        return cancelledKeys;

    }

    /**

     * Registers the given channel with this selector.

     *

     * <p> This method is invoked by a channel's {@link

     * AbstractSelectableChannel#register register} method in order to perform

     * the actual work of registering the channel with this selector.  </p>

     *

     * @param  ch

     *         The channel to be registered

     *

     * @param  ops

     *         The initial interest set, which must be valid

     *

     * @param  att

     *         The initial attachment for the resulting key

     *

     * @return  A new key representing the registration of the given channel

     *          with this selector

     */

    protected abstract SelectionKey register(AbstractSelectableChannel ch,

                                             int ops, Object att);

    /**

     * Removes the given key from its channel's key set.

     *

     * <p> This method must be invoked by the selector for each channel that it

     * deregisters.  </p>

     *

     * @param  key

     *         The selection key to be removed

     */

    protected final void deregister(AbstractSelectionKey key) {

        ((AbstractSelectableChannel)key.channel()).removeKey(key);

    }

    // -- Interruption machinery --

    private Interruptible interruptor = null;

    /**

     * Marks the beginning of an I/O operation that might block indefinitely.

     *

     * <p> This method should be invoked in tandem with the {@link #end end}

     * method, using a {@code try} ... {@code finally} block as

     * shown <a href="#be">above</a>, in order to implement interruption for

     * this selector.

     *

     * <p> Invoking this method arranges for the selector's {@link

     * Selector#wakeup wakeup} method to be invoked if a thread's {@link

     * Thread#interrupt interrupt} method is invoked while the thread is

     * blocked in an I/O operation upon the selector.  </p>

     */

    protected final void begin() {

        if (interruptor == null) {

            interruptor = new Interruptible() {

                    public void interrupt(Thread ignore) {

                        AbstractSelector.this.wakeup();

                    }};

        }

        AbstractInterruptibleChannel.blockedOn(interruptor);

        Thread me = Thread.currentThread();

        if (me.isInterrupted())

            interruptor.interrupt(me);

    }

    /**

     * Marks the end of an I/O operation that might block indefinitely.

     *

     * <p> This method should be invoked in tandem with the {@link #begin begin}

     * method, using a {@code try} ... {@code finally} block as

     * shown <a href="#be">above</a>, in order to implement interruption for

     * this selector.  </p>

     */

    protected final void end() {

        AbstractInterruptibleChannel.blockedOn(null);

    }

}