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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
   * 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
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   */
  
  package java.nio.channels;
  
  import java.nio.ByteBuffer;
  import java.util.concurrent.Future;
  
  /**
   * An asynchronous channel that can read and write bytes.
   *
   * <p> Some channels may not allow more than one read or write to be outstanding
   * at any given time. If a thread invokes a read method before a previous read
   * operation has completed then a {@link ReadPendingException} will be thrown.
   * Similarly, if a write method is invoked before a previous write has completed
   * then {@link WritePendingException} is thrown. Whether or not other kinds of
   * I/O operations may proceed concurrently with a read operation depends upon
   * the type of the channel.
   *
   * <p> Note that {@link ByteBuffer ByteBuffers} are not safe for use by
   * multiple concurrent threads. When a read or write operation is initiated then
   * care must be taken to ensure that the buffer is not accessed until the
   * operation completes.
   *
   * @see Channels#newInputStream(AsynchronousByteChannel)
   * @see Channels#newOutputStream(AsynchronousByteChannel)
   *
   * @since 1.7
   */
  
  public interface AsynchronousByteChannel
      extends AsynchronousChannel
  {
      /**
       * Reads a sequence of bytes from this channel into the given buffer.
       *
       * <p> This method initiates an asynchronous read operation to read a
       * sequence of bytes from this channel into the given buffer. The {@code
       * handler} parameter is a completion handler that is invoked when the read
       * operation completes (or fails). The result passed to the completion
       * handler is the number of bytes read or {@code -1} if no bytes could be
       * read because the channel has reached end-of-stream.
       *
       * <p> The read operation may read up to <i>r</i> bytes from the channel,
       * where <i>r</i> is the number of bytes remaining in the buffer, that is,
       * {@code dst.remaining()} at the time that the read is attempted. Where
       * <i>r</i> is 0, the read operation completes immediately with a result of
       * {@code 0} without initiating an I/O operation.
       *
       * <p> Suppose that a byte sequence of length <i>n</i> is read, where
       * <tt>0</tt>&nbsp;<tt>&lt;</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;<i>r</i>.
       * This byte sequence will be transferred into the buffer so that the first
       * byte in the sequence is at index <i>p</i> and the last byte is at index
       * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>&nbsp;<tt>-</tt>&nbsp;<tt>1</tt>,
       * where <i>p</i> is the buffer's position at the moment the read is
       * performed. Upon completion the buffer's position will be equal to
       * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>; its limit will not have changed.
       *
       * <p> Buffers are not safe for use by multiple concurrent threads so care
       * should be taken to not access the buffer until the operation has
       * completed.
       *
       * <p> This method may be invoked at any time. Some channel types may not
       * allow more than one read to be outstanding at any given time. If a thread
       * initiates a read operation before a previous read operation has
       * completed then a {@link ReadPendingException} will be thrown.
       *
       * @param   <A>
       *          The type of the attachment
       * @param   dst
       *          The buffer into which bytes are to be transferred
       * @param   attachment
       *          The object to attach to the I/O operation; can be {@code null}
       * @param   handler
       *          The completion handler
       *
       * @throws  IllegalArgumentException
       *          If the buffer is read-only
       * @throws  ReadPendingException
       *          If the channel does not allow more than one read to be outstanding
       *          and a previous read has not completed
       * @throws  ShutdownChannelGroupException
       *          If the channel is associated with a {@link AsynchronousChannelGroup
       *          group} that has terminated
       */
      <A> void read(ByteBuffer dst,
                    A attachment,
                    CompletionHandler<Integer,? super A> handler);
  
      /**
       * Reads a sequence of bytes from this channel into the given buffer.
       *
       * <p> This method initiates an asynchronous read operation to read a
       * sequence of bytes from this channel into the given buffer. The method
       * behaves in exactly the same manner as the {@link
       * #read(ByteBuffer,Object,CompletionHandler)
       * read(ByteBuffer,Object,CompletionHandler)} method except that instead
       * of specifying a completion handler, this method returns a {@code Future}
       * representing the pending result. The {@code Future}'s {@link Future#get()
       * get} method returns the number of bytes read or {@code -1} if no bytes
       * could be read because the channel has reached end-of-stream.
       *
       * @param   dst
       *          The buffer into which bytes are to be transferred
       *
       * @return  A Future representing the result of the operation
       *
       * @throws  IllegalArgumentException
       *          If the buffer is read-only
       * @throws  ReadPendingException
       *          If the channel does not allow more than one read to be outstanding
       *          and a previous read has not completed
       */
      Future<Integer> read(ByteBuffer dst);
  
      /**
       * Writes a sequence of bytes to this channel from the given buffer.
       *
       * <p> This method initiates an asynchronous write operation to write a
       * sequence of bytes to this channel from the given buffer. The {@code
       * handler} parameter is a completion handler that is invoked when the write
       * operation completes (or fails). The result passed to the completion
       * handler is the number of bytes written.
       *
       * <p> The write operation may write up to <i>r</i> bytes to the channel,
       * where <i>r</i> is the number of bytes remaining in the buffer, that is,
       * {@code src.remaining()} at the time that the write is attempted. Where
       * <i>r</i> is 0, the write operation completes immediately with a result of
       * {@code 0} without initiating an I/O operation.
       *
       * <p> Suppose that a byte sequence of length <i>n</i> is written, where
       * <tt>0</tt>&nbsp;<tt>&lt;</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;<i>r</i>.
       * This byte sequence will be transferred from the buffer starting at index
       * <i>p</i>, where <i>p</i> is the buffer's position at the moment the
       * write is performed; the index of the last byte written will be
       * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>&nbsp;<tt>-</tt>&nbsp;<tt>1</tt>.
       * Upon completion the buffer's position will be equal to
       * <i>p</i>&nbsp;<tt>+</tt>&nbsp;<i>n</i>; its limit will not have changed.
       *
       * <p> Buffers are not safe for use by multiple concurrent threads so care
       * should be taken to not access the buffer until the operation has
       * completed.
       *
       * <p> This method may be invoked at any time. Some channel types may not
       * allow more than one write to be outstanding at any given time. If a thread
       * initiates a write operation before a previous write operation has
       * completed then a {@link WritePendingException} will be thrown.
       *
       * @param   <A>
       *          The type of the attachment
       * @param   src
       *          The buffer from which bytes are to be retrieved
       * @param   attachment
       *          The object to attach to the I/O operation; can be {@code null}
       * @param   handler
       *          The completion handler object
       *
       * @throws  WritePendingException
       *          If the channel does not allow more than one write to be outstanding
       *          and a previous write has not completed
       * @throws  ShutdownChannelGroupException
       *          If the channel is associated with a {@link AsynchronousChannelGroup
       *          group} that has terminated
       */
      <A> void write(ByteBuffer src,
                     A attachment,
                     CompletionHandler<Integer,? super A> handler);
  
      /**
       * Writes a sequence of bytes to this channel from the given buffer.
       *
       * <p> This method initiates an asynchronous write operation to write a
       * sequence of bytes to this channel from the given buffer. The method
       * behaves in exactly the same manner as the {@link
       * #write(ByteBuffer,Object,CompletionHandler)
       * write(ByteBuffer,Object,CompletionHandler)} method except that instead
       * of specifying a completion handler, this method returns a {@code Future}
       * representing the pending result. The {@code Future}'s {@link Future#get()
       * get} method returns the number of bytes written.
       *
       * @param   src
       *          The buffer from which bytes are to be retrieved
       *
       * @return A Future representing the result of the operation
       *
       * @throws  WritePendingException
       *          If the channel does not allow more than one write to be outstanding
       *          and a previous write has not completed
       */
      Future<Integer> write(ByteBuffer src);
  }
  