/*

 * Copyright (c) 2007, 2009, Oracle and/or its affiliates. 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.  Oracle designates this

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

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.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>void <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 or fails.

 *

 * <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. This causes all threads waiting on the result of

 * the I/O operation to throw {@link java.util.concurrent.CancellationException}.

 * Whether the underlying I/O operation can be cancelled is highly implementation

 * specific and therefore not specified. Where cancellation leaves 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 that are <i>similar</i>

 * to the operation that was cancelled. 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 an error state; further

 * attempts to initiate a {@code read} operation cause an unspecified runtime

 * exception to be thrown. Similarly, if a write operation is cancelled but the

 * implementation cannot guarantee that bytes have not been written to the

 * channel then subsequent attempts to initiate a {@code write} will fail with

 * an unspecified runtime exception.

 *

 * <p> Where the {@link Future#cancel 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. In that case all threads waiting

 * on the result of the I/O operation throw {@code CancellationException} and

 * any other I/O operations outstanding on the channel complete with the

 * exception {@link AsynchronousCloseException}.

 *

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

 * operations then it is 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, 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;

}