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    
019    package org.apache.hadoop.mapred;
020    
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import 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
036    public 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    }