/*

 * Copyright 2007-2009 Sun Microsystems, Inc.  All Rights Reserved.

 * 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

 * published by the Free Software Foundation.  Sun designates this

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

 * by Sun in the LICENSE file that accompanied this code.

 *

 * 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.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.nio.channels;

import java.io.IOException;

import java.util.concurrent.Future;  // javadoc

/**

 * A channel that supports asynchronous I/O operations. Asynchronous I/O

 * operations will usually take one of two forms:

 *

 * <ol>

 * <li><pre>{@link Future}&lt;V&gt; <em>operation</em>(<em>...</em>)</pre></li>

 * <li><pre>Future&lt;V&gt; <em>operation</em>(<em>...</em> A attachment, {@link CompletionHandler}&lt;V,? super A&gt handler)</pre></li>

 * </ol>

 *

 * where <i>operation</i> is the name of the I/O operation (read or write for

 * example), <i>V</i> is the result type of the I/O operation, and <i>A</i> is

 * the type of an object attached to the I/O operation to provide context when

 * consuming the result. The attachment is important for cases where a

 * <em>state-less</em> {@code CompletionHandler} is used to consume the result

 * of many I/O operations.

 *

 * <p> In the first form, the methods defined by the {@link Future Future}

 * interface may be used to check if the operation has completed, wait for its

 * completion, and to retrieve the result. In the second form, a {@link

 * CompletionHandler} is invoked to consume the result of the I/O operation when

 * it completes, fails, or is cancelled.

 *

 * <p> A channel that implements this interface is <em>asynchronously

 * closeable</em>: If an I/O operation is outstanding on the channel and the

 * channel's {@link #close close} method is invoked, then the I/O operation

 * fails with the exception {@link AsynchronousCloseException}.

 *

 * <p> Asynchronous channels are safe for use by multiple concurrent threads.

 * Some channel implementations may support concurrent reading and writing, but

 * may not allow more than one read and one write operation to be outstanding at

 * any given time.

 *

 * <h4>Cancellation</h4>

 *

 * <p> The {@code Future} interface defines the {@link Future#cancel cancel}

 * method to cancel execution of a task.

 *

 * <p> Where the {@code cancel} method is invoked with the {@code

 * mayInterruptIfRunning} parameter set to {@code true} then the I/O operation

 * may be interrupted by closing the channel. This will cause any other I/O

 * operations outstanding on the channel to complete with the exception {@link

 * AsynchronousCloseException}.

 *

 * <p> If a {@code CompletionHandler} is specified when initiating an I/O

 * operation, and the {@code cancel} method is invoked to cancel the I/O

 * operation before it completes, then the {@code CompletionHandler}'s {@link

 * CompletionHandler#cancelled cancelled} method is invoked.

 *

 * <p> If an implementation of this interface supports a means to cancel I/O

 * operations, and where cancellation may leave the channel, or the entity to

 * which it is connected, in an inconsistent state, then the channel is put into

 * an implementation specific <em>error state</em> that prevents further

 * attempts to initiate I/O operations on the channel. For example, if a read

 * operation is cancelled but the implementation cannot guarantee that bytes

 * have not been read from the channel then it puts the channel into error state

 * state; further attempts to initiate a {@code read} operation causes an

 * unspecified runtime exception to be thrown.

 *

 * <p> Where the {@code cancel} method is invoked to cancel read or write

 * operations then it recommended that all buffers used in the I/O operations be

 * discarded or care taken to ensure that the buffers are not accessed while the

 * channel remains open.

 *

 *  @since 1.7

 */

public interface AsynchronousChannel

    extends Channel

{

    /**

     * Closes this channel.

     *

     * <p> Any outstanding asynchronous operations upon this channel will

     * complete with the exception {@link AsynchronousCloseException}. After a

     * channel is closed then further attempts to initiate asynchronous I/O

     * operations complete immediately with cause {@link ClosedChannelException}.

     *

     * <p>  This method otherwise behaves exactly as specified by the {@link

     * Channel} interface.

     *

     * @throws  IOException

     *          If an I/O error occurs

     */

    @Override

    void close() throws IOException;

}