Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||
AggregatorWriter |
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| 1.0;1 |
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.graph; | |
20 | ||
21 | import java.io.IOException; | |
22 | import java.util.Map.Entry; | |
23 | ||
24 | import org.apache.hadoop.io.Writable; | |
25 | import org.apache.hadoop.mapreduce.Mapper.Context; | |
26 | ||
27 | /** | |
28 | * An AggregatorWriter is used to export Aggregators during or at the end of | |
29 | * each computation. It runs on the master and it's called at the end of each | |
30 | * superstep. The special signal {@link AggregatorWriter#LAST_SUPERSTEP} is | |
31 | * passed to {@link AggregatorWriter#writeAggregator(Iterable, long)} as the | |
32 | * superstep value to signal the end of computation. | |
33 | */ | |
34 | public interface AggregatorWriter { | |
35 | /** Signal for last superstep */ | |
36 | int LAST_SUPERSTEP = -1; | |
37 | ||
38 | /** | |
39 | * The method is called at the initialization of the AggregatorWriter. | |
40 | * More precisely, the aggregatorWriter is initialized each time a new | |
41 | * master is elected. | |
42 | * | |
43 | * @param context Mapper Context where the master is running on | |
44 | * @param applicationAttempt ID of the applicationAttempt, used to | |
45 | * disambiguate aggregator writes for different attempts | |
46 | * @throws IOException | |
47 | */ | |
48 | @SuppressWarnings("rawtypes") | |
49 | void initialize(Context context, long applicationAttempt) throws IOException; | |
50 | ||
51 | /** | |
52 | * The method is called at the end of each superstep. The user might decide | |
53 | * whether to write the aggregators values for the current superstep. For | |
54 | * the last superstep, {@link AggregatorWriter#LAST_SUPERSTEP} is passed. | |
55 | * | |
56 | * @param aggregatorMap Map from aggregator name to aggregator value | |
57 | * @param superstep Current superstep | |
58 | * @throws IOException | |
59 | */ | |
60 | void writeAggregator( | |
61 | Iterable<Entry<String, Writable>> aggregatorMap, | |
62 | long superstep) throws IOException; | |
63 | ||
64 | /** | |
65 | * The method is called at the end of a successful computation. The method | |
66 | * is not called when the job fails and a new master is elected. For this | |
67 | * reason it's advised to flush data at the end of | |
68 | * {@link AggregatorWriter#writeAggregator(Iterable, long)}. | |
69 | * | |
70 | * @throws IOException | |
71 | */ | |
72 | void close() throws IOException; | |
73 | } |