content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.client;
  
  import java.io.IOException;
  
  /**
   * Stream that permits positional reading.
   */
  public interface PositionedReadable {
    /**
     * Reads up to the specified number of bytes, from a given position within a file, and return the
     * number of bytes read. This does not change the current offset of a file, and is thread-safe.
     *
     * Not all implementations meet the thread safety requirement. According to the documentation of
     * the PositionedReadable interface in Hadoop, those that do not meet the requirement cannot
     * be used as a backing store for some applications, such as Apache HBase.
     *
     * All implementations of this interface in Alluxio must meet the thread safety requirement.
     *
     * @param position position within file
     * @param buffer destination buffer
     * @param offset offset in the buffer
     * @param length number of bytes to read
     * @return actual number of bytes read; -1 means "EOF";
     */
    int positionedRead(long position, byte[] buffer, int offset, int length) throws IOException;
  }
  