src/java/org/apache/hadoop/mapred/BufferSorter.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;

import org.apache.hadoop.io.OutputBuffer;
import org.apache.hadoop.io.SequenceFile.Sorter.RawKeyValueIterator;
import org.apache.hadoop.util.Progressable;

/** This class provides a generic sort interface that should be implemented
 * by specific sort algorithms. The use case is the following:
 * A user class writes key/value records to a buffer, and finally wants to
 * sort the buffer. This interface defines methods by which the user class
 * can update the interface implementation with the offsets of the records
 * and the lengths of the keys/values. The user class gives a reference to
 * the buffer when the latter wishes to sort the records written to the buffer
 * so far. Typically, the user class decides the point at which sort should
 * happen based on the memory consumed so far by the buffer and the data
 * structures maintained by an implementation of this interface. That is why
 * a method is provided to get the memory consumed so far by the datastructures
 * in the interface implementation.  
 */
interface BufferSorter extends JobConfigurable {
  
  /** Pass the Progressable object so that sort can call progress while it is sorting
   * @param reporter the Progressable object reference
   */
  public void setProgressable(Progressable reporter);
    
  /** When a key/value is added at a particular offset in the key/value buffer, 
   * this method is invoked by the user class so that the impl of this sort 
   * interface can update its datastructures. 
   * @param recordOffset the offset of the key in the buffer
   * @param keyLength the length of the key
   * @param valLength the length of the val in the buffer
   */
  public void addKeyValue(int recordoffset, int keyLength, int valLength);
  
  /** The user class invokes this method to set the buffer that the specific 
   * sort algorithm should "indirectly" sort (generally, sort algorithm impl 
   * should access this buffer via comparators and sort offset-indices to the
   * buffer).
   * @param buffer the map output buffer
   */
  public void setInputBuffer(OutputBuffer buffer);
  
  /** The framework invokes this method to get the memory consumed so far
   * by an implementation of this interface.
   * @return memoryUsed in bytes 
   */
  public long getMemoryUtilized();
  
  /** Framework decides when to actually sort
   */
  public RawKeyValueIterator sort();
  
  /** Framework invokes this to signal the sorter to cleanup
   */
  public void close();
}