branch-2.0.4-alpha/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/pipes/PipesPartitioner.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.mapred.pipes;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.Partitioner;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * This partitioner is one that can either be set manually per a record or it
 * can fall back onto a Java partitioner that was set by the user.
 */
class PipesPartitioner<K extends WritableComparable,
                       V extends Writable>
  implements Partitioner<K, V> {
  
  private static ThreadLocal<Integer> cache = new ThreadLocal<Integer>();
  private Partitioner<K, V> part = null;
  
  @SuppressWarnings("unchecked")
  public void configure(JobConf conf) {
    part =
      ReflectionUtils.newInstance(Submitter.getJavaPartitioner(conf), conf);
  }

  /**
   * Set the next key to have the given partition.
   * @param newValue the next partition value
   */
  static void setNextPartition(int newValue) {
    cache.set(newValue);
  }

  /**
   * If a partition result was set manually, return it. Otherwise, we call
   * the Java partitioner.
   * @param key the key to partition
   * @param value the value to partition
   * @param numPartitions the number of reduces
   */
  public int getPartition(K key, V value, 
                          int numPartitions) {
    Integer result = cache.get();
    if (result == null) {
      return part.getPartition(key, value, numPartitions);
    } else {
      return result;
    }
  }

}