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MinMessageCombiner xref
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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  }