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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   * This code is free software; you can redistribute it and/or modify it
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   * 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
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  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.
   *
   * <h2>Cancellation</h2>
   *
   * <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;
  }
  