hadoop ReplicaAccessor 源码

haddop ReplicaAccessor 代码

文件路径：/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/ReplicaAccessor.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hdfs;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * The public API for ReplicaAccessor objects.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class ReplicaAccessor {
  /**
   * Read bytes from the replica.
   *
   * @param pos    The position in the replica to start reading at.
   *                 Must not be negative.
   * @param buf    The byte array to read into.
   * @param off    The offset within buf to start reading into.
   * @param len    The maximum length to read.
   *
   * @return       The number of bytes read.  If the read extends past the end
   *                  of the replica, a short read count will be returned.  We
   *                  will should return -1 if EOF is reached and no bytes
   *                  can be returned.  We will never return a short read
   *                  count unless EOF is reached.
   */
  public abstract int read(long pos, byte[] buf, int off, int len)
      throws IOException;

  /**
   * Read bytes from the replica.
   *
   * @param pos    The position in the replica to start reading at.
   *                 Must not be negative.
   * @param buf    The byte buffer to read into.  The amount to read will be
   *                 dictated by the remaining bytes between the current
   *                 position and the limit.  The ByteBuffer may or may not be
   *                 direct.
   *
   * @return       The number of bytes read.  If the read extends past the end
   *                 of the replica, a short read count will be returned.  We
   *                 should return -1 if EOF is reached and no bytes can be
   *                 returned.  We will never return a short read count unless
   *                 EOF is reached.
   */
  public abstract int read(long pos, ByteBuffer buf) throws IOException;

  /**
   * Release the resources associated with the ReplicaAccessor.
   *
   * It is recommended that implementations never throw an IOException.  The
   * method is declared as throwing IOException in order to remain compatible
   * with java.io.Closeable.  If an exception is thrown, the ReplicaAccessor
   * must still be closed when the function returns in order to prevent a
   * resource leak.
   */
  public abstract void close() throws IOException;

  /**
   * Return true if bytes read via this accessor should count towards the
   * local byte count statistics.
   */
  public abstract boolean isLocal();

  /**
   * Return true if bytes read via this accessor should count towards the
   * short-circuit byte count statistics.
   */
  public abstract boolean isShortCircuit();

  /**
   * Return the network distance between local machine and the remote machine.
   */
  public int getNetworkDistance() {
    return isLocal() ? 0 : Integer.MAX_VALUE;
  }
}

相关信息

hadoop 源码目录

相关文章

hadoop AddBlockFlag 源码

hadoop BlockMissingException 源码

hadoop BlockReader 源码

hadoop CannotObtainBlockLengthException 源码

hadoop ClientContext 源码

hadoop ClientGSIContext 源码

hadoop DFSClient 源码

hadoop DFSClientFaultInjector 源码

hadoop DFSHedgedReadMetrics 源码

hadoop DFSInotifyEventInputStream 源码