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.aggregators; 20 21 import java.io.IOException; 22 import java.util.Map.Entry; 23 24 import org.apache.giraph.conf.ImmutableClassesGiraphConfigurable; 25 import org.apache.hadoop.io.Writable; 26 import org.apache.hadoop.mapreduce.Mapper.Context; 27 28 /** 29 * An AggregatorWriter is used to export Aggregators during or at the end of 30 * each computation. It runs on the master and it's called at the end of each 31 * superstep. The special signal {@link AggregatorWriter#LAST_SUPERSTEP} is 32 * passed to {@link AggregatorWriter#writeAggregator(Iterable, long)} as the 33 * superstep value to signal the end of computation. 34 */ 35 public interface AggregatorWriter extends ImmutableClassesGiraphConfigurable { 36 /** Signal for last superstep */ 37 int LAST_SUPERSTEP = -1; 38 39 /** 40 * The method is called at the initialization of the AggregatorWriter. 41 * More precisely, the aggregatorWriter is initialized each time a new 42 * master is elected. 43 * 44 * @param context Mapper Context where the master is running on 45 * @param applicationAttempt ID of the applicationAttempt, used to 46 * disambiguate aggregator writes for different attempts 47 * @throws IOException 48 */ 49 @SuppressWarnings("rawtypes") 50 void initialize(Context context, long applicationAttempt) throws IOException; 51 52 /** 53 * The method is called at the end of each superstep. The user might decide 54 * whether to write the aggregators values for the current superstep. For 55 * the last superstep, {@link AggregatorWriter#LAST_SUPERSTEP} is passed. 56 * 57 * @param aggregatorMap Map from aggregator name to aggregator value 58 * @param superstep Current superstep 59 * @throws IOException 60 */ 61 void writeAggregator( 62 Iterable<Entry<String, Writable>> aggregatorMap, 63 long superstep) throws IOException; 64 65 /** 66 * The method is called at the end of a successful computation. The method 67 * is not called when the job fails and a new master is elected. For this 68 * reason it's advised to flush data at the end of 69 * {@link AggregatorWriter#writeAggregator(Iterable, long)}. 70 * 71 * @throws IOException 72 */ 73 void close() throws IOException; 74 }