1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.giraph.combiner; 20 21 import org.apache.hadoop.io.Writable; 22 import org.apache.hadoop.io.WritableComparable; 23 24 /** 25 * Abstract class to extend for combining messages sent to the same vertex. 26 * MessageCombiner for applications where each two messages for one 27 * vertex can be combined into one. 28 * 29 * @param <I> Vertex id 30 * @param <M> Message data 31 */ 32 public interface MessageCombiner<I extends WritableComparable, 33 M extends Writable> { 34 /** 35 * Combine messageToCombine with originalMessage, by modifying 36 * originalMessage. Note that the messageToCombine object 37 * may be reused by the infrastructure, therefore, you cannot directly 38 * use it or any objects from it in original message 39 * 40 * @param vertexIndex Index of the vertex getting these messages 41 * @param originalMessage The first message which we want to combine; 42 * put the result of combining in this message 43 * @param messageToCombine The second message which we want to combine 44 * (object may be reused - do not reference it or its 45 * member objects) 46 */ 47 void combine(I vertexIndex, M originalMessage, 48 M messageToCombine); 49 50 /** 51 * Get the initial message. When combined with any other message M, 52 * the result should be M. 53 * 54 * @return Initial message 55 */ 56 M createInitialMessage(); 57 }