001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapred;
020
021import java.io.IOException;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * Expert: Generic interface for {@link Mapper}s.
028 * 
029 * <p>Custom implementations of <code>MapRunnable</code> can exert greater 
030 * control on map processing e.g. multi-threaded, asynchronous mappers etc.</p>
031 * 
032 * @see Mapper
033 */
034@InterfaceAudience.Public
035@InterfaceStability.Stable
036public interface MapRunnable<K1, V1, K2, V2>
037    extends JobConfigurable {
038  
039  /** 
040   * Start mapping input <tt>&lt;key, value&gt;</tt> pairs.
041   *  
042   * <p>Mapping of input records to output records is complete when this method 
043   * returns.</p>
044   * 
045   * @param input the {@link RecordReader} to read the input records.
046   * @param output the {@link OutputCollector} to collect the outputrecords.
047   * @param reporter {@link Reporter} to report progress, status-updates etc.
048   * @throws IOException
049   */
050  void run(RecordReader<K1, V1> input, OutputCollector<K2, V2> output,
051           Reporter reporter)
052    throws IOException;
053}