Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||
ReduceOperation |
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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 | package org.apache.giraph.reducers; | |
19 | ||
20 | import org.apache.hadoop.io.Writable; | |
21 | ||
22 | /** | |
23 | * Reduce operations defining how to reduce single values | |
24 | * passed on workers, into partial values on workers, and then | |
25 | * into a single global reduced value. | |
26 | * | |
27 | * Object should be thread safe. Most frequently it should be | |
28 | * immutable object, so that functions can execute concurrently. | |
29 | * Rarely when object is mutable | |
30 | * ({@link org.apache.giraph.master.AggregatorReduceOperation}), | |
31 | * i.e. stores reusable object inside, accesses should be synchronized. | |
32 | * | |
33 | * @param <S> Single value type, objects passed on workers | |
34 | * @param <R> Reduced value type | |
35 | */ | |
36 | public interface ReduceOperation<S, R extends Writable> extends Writable { | |
37 | /** | |
38 | * Return new reduced value which is neutral to reduce operation. | |
39 | * | |
40 | * @return Neutral value | |
41 | */ | |
42 | R createInitialValue(); | |
43 | /** | |
44 | * Add a new value. | |
45 | * Needs to be commutative and associative | |
46 | * | |
47 | * Commonly, returned value should be same as curValue argument. | |
48 | * | |
49 | * @param curValue Partial value into which to reduce and store the result | |
50 | * @param valueToReduce Single value to be reduced | |
51 | * @return reduced value | |
52 | */ | |
53 | R reduce(R curValue, S valueToReduce); | |
54 | /** | |
55 | * Add partially reduced value to current partially reduced value. | |
56 | * | |
57 | * Commonly, returned value should be same as curValue argument. | |
58 | * | |
59 | * @param curValue Partial value into which to reduce and store the result | |
60 | * @param valueToReduce Partial value to be reduced | |
61 | * @return reduced value | |
62 | */ | |
63 | R reduceMerge(R curValue, R valueToReduce); | |
64 | } |