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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the License. You may obtain a copy of the License at:
    7    *
    8    *   http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  package org.jboss.netty.channel;
    17
    18  import java.io.IOException;
    19  import java.nio.channels.FileChannel;
    20  import java.nio.channels.WritableByteChannel;
    21
    22  import org.jboss.netty.util.ExternalResourceReleasable;
    23
    24  /**
    25   * A region of a file that is sent via a {@link Channel} which supports
    26   * <a href="http://en.wikipedia.org/wiki/Zero-copy">zero-copy file transfer</a>.
    27   *
    28   * <h3>Upgrade your JDK / JRE</h3>
    29   *
    30   * {@link FileChannel#transferTo(long, long, WritableByteChannel)} has at least
    31   * four known bugs in the old versions of Sun JDK and perhaps its derived ones.
    32   * Please upgrade your JDK to 1.6.0_18 or later version if you are going to use
    33   * zero-copy file transfer.
    34   * <ul>
    35   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5103988">5103988</a>
    36   *   - FileChannel.transferTo() should return -1 for EAGAIN instead throws IOException</li>
    37   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6253145">6253145</a>
    38   *   - FileChannel.transferTo() on Linux fails when going beyond 2GB boundary</li>
    39   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6427312">6427312</a>
    40   *   - FileChannel.transferTo() throws IOException "system call interrupted"</li>
    41   * <li><a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6524172">6470086</a>
    42   *   - FileChannel.transferTo(2147483647, 1, channel) causes "Value too large" exception</li>
    43   * </ul>
    44   *
    45   * <h3>Check your operating system and JDK / JRE</h3>
    46   *
    47   * If your operating system (or JDK / JRE) does not support zero-copy file
    48   * transfer, sending a file with {@link FileRegion} might fail or yield worse
    49   * performance.  For example, sending a large file doesn't work well in Windows.
    50   *
    51   * <h3>Not all transports support it</h3>
    52   *
    53   * Currently, the NIO transport is the only transport that supports {@link FileRegion}.
    54   * Attempting to write a {@link FileRegion} to non-NIO {@link Channel} will trigger
    55   * a {@link ClassCastException} or a similar exception.
    56   */
    57  public interface FileRegion extends ExternalResourceReleasable {
    58
    59      // FIXME Make sure all transports support writing a FileRegion
    60      //       Even if zero copy cannot be achieved, all transports should emulate it.
    61
    62      /**
    63       * Returns the offset in the file where the transfer began.
    64       */
    65      long getPosition();
    66
    67      /**
    68       * Returns the number of bytes to transfer.
    69       */
    70      long getCount();
    71
    72      /**
    73       * Transfers the content of this file region to the specified channel.
    74       *
    75       * @param target    the destination of the transfer
    76       * @param position  the relative offset of the file where the transfer
    77       *                  begins from.  For example, <tt>0</tt> will make the
    78       *                  transfer start from {@link #getPosition()}th byte and
    79       *                  <tt>{@link #getCount()} - 1</tt> will make the last
    80       *                  byte of the region transferred.
    81       */
    82      long transferTo(WritableByteChannel target, long position) throws IOException;
    83  }