hdfs/src/java/org/apache/hadoop/hdfs/server/protocol/BlockRecoveryCommand.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.server.protocol;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Collection;
import java.util.ArrayList;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.hdfs.protocol.LocatedBlock;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableFactories;
import org.apache.hadoop.io.WritableFactory;

/**
 * BlockRecoveryCommand is an instruction to a data-node to recover
 * the specified blocks.
 *
 * The data-node that receives this command treats itself as a primary
 * data-node in the recover process.
 *
 * Block recovery is identified by a recoveryId, which is also the new
 * generation stamp, which the block will have after the recovery succeeds.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class BlockRecoveryCommand extends DatanodeCommand {
  Collection<RecoveringBlock> recoveringBlocks;

  /**
   * This is a block with locations from which it should be recovered
   * and the new generation stamp, which the block will have after 
   * successful recovery.
   * 
   * The new generation stamp of the block, also plays role of the recovery id.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public static class RecoveringBlock extends LocatedBlock {
    private long newGenerationStamp;

    /**
     * Create empty RecoveringBlock.
     */
    public RecoveringBlock() {
      super();
      newGenerationStamp = -1L;
    }

    /**
     * Create RecoveringBlock.
     */
    public RecoveringBlock(Block b, DatanodeInfo[] locs, long newGS) {
      super(b, locs, -1, false); // startOffset is unknown
      this.newGenerationStamp = newGS;
    }

    /**
     * Return the new generation stamp of the block,
     * which also plays role of the recovery id.
     */
    public long getNewGenerationStamp() {
      return newGenerationStamp;
    }

    ///////////////////////////////////////////
    // Writable
    ///////////////////////////////////////////
    static {                                      // register a ctor
      WritableFactories.setFactory
        (RecoveringBlock.class,
         new WritableFactory() {
           public Writable newInstance() { return new RecoveringBlock(); }
         });
    }

    public void write(DataOutput out) throws IOException {
      super.write(out);
      out.writeLong(newGenerationStamp);
    }

    public void readFields(DataInput in) throws IOException {
      super.readFields(in);
      newGenerationStamp = in.readLong();
    }
  }

  /**
   * Create empty BlockRecoveryCommand.
   */
  public BlockRecoveryCommand() {
    this(0);
  }

  /**
   * Create BlockRecoveryCommand with
   * the specified capacity for recovering blocks.
   */
  public BlockRecoveryCommand(int capacity) {
    super(DatanodeProtocol.DNA_RECOVERBLOCK);
    recoveringBlocks = new ArrayList<RecoveringBlock>(capacity);
  }

  /**
   * Return the list of recovering blocks.
   */
  public Collection<RecoveringBlock> getRecoveringBlocks() {
    return recoveringBlocks;
  }

  /**
   * Add recovering block to the command.
   */
  public void add(RecoveringBlock block) {
    recoveringBlocks.add(block);
  }

  ///////////////////////////////////////////
  // Writable
  ///////////////////////////////////////////
  static {                                      // register a ctor
    WritableFactories.setFactory
      (BlockRecoveryCommand.class,
       new WritableFactory() {
         public Writable newInstance() { return new BlockRecoveryCommand(); }
       });
  }

  public void write(DataOutput out) throws IOException {
    super.write(out);
    out.writeInt(recoveringBlocks.size());
    for(RecoveringBlock block : recoveringBlocks) {
      block.write(out);
    }
  }

  public void readFields(DataInput in) throws IOException {
    super.readFields(in);
    int numBlocks = in.readInt();
    recoveringBlocks = new ArrayList<RecoveringBlock>(numBlocks);
    for(int i = 0; i < numBlocks; i++) {
      RecoveringBlock b = new RecoveringBlock();
      b.readFields(in);
      add(b);
    }
  }
}