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 package org.apache.giraph.combiner; 19 20 import org.apache.giraph.types.ops.NumericTypeOps; 21 import org.apache.hadoop.io.Writable; 22 import org.apache.hadoop.io.WritableComparable; 23 24 /** 25 * Keeps only the message with minimum value. 26 * 27 * @param <I> Vertex id 28 * @param <M> Message 29 */ 30 public class MinMessageCombiner<I extends WritableComparable, 31 M extends Writable> implements MessageCombiner<I, M> { 32 /** Numeric type ops for the value to combine */ 33 private final NumericTypeOps<M> numTypeOps; 34 35 /** 36 * Combiner 37 * 38 * @param numTypeOps Type ops to use 39 */ 40 public MinMessageCombiner(NumericTypeOps<M> numTypeOps) { 41 this.numTypeOps = numTypeOps; 42 } 43 44 @Override 45 public void combine(I vertexId, M originalMessage, M messageToCombine) { 46 if (numTypeOps.compare(originalMessage, messageToCombine) > 0) { 47 numTypeOps.set(originalMessage, messageToCombine); 48 } 49 } 50 51 @Override 52 public M createInitialMessage() { 53 return this.numTypeOps.createMaxPositiveValue(); 54 } 55 }