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PseudoRandomIntNullLocalEdgesHelper 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  
19  package org.apache.giraph.io.formats;
20  
21  import org.apache.giraph.conf.ImmutableClassesGiraphConfiguration;
22  import org.apache.giraph.partition.PartitionUtils;
23  import org.apache.giraph.worker.WorkerInfo;
24  
25  import java.util.Collections;
26  import java.util.List;
27  import java.util.Random;
28  
29  /**
30   * Helper class to generate pseudo-random local edges.
31   * Like {@link PseudoRandomLocalEdgesHelper}, but for graphs where vertex ids
32   * are integers.
33   */
34  public class PseudoRandomIntNullLocalEdgesHelper {
35    /** Minimum ratio of partition-local edges. */
36    private float minLocalEdgesRatio;
37    /** Total number of vertices. */
38    private int numVertices;
39    /** Total number of partitions. */
40    private int numPartitions;
41    /** Average partition size. */
42    private int partitionSize;
43  
44    /**
45     * Constructor.
46     *
47     * @param numVertices        Total number of vertices.
48     * @param conf               Configuration.
49     */
50    public PseudoRandomIntNullLocalEdgesHelper(int numVertices,
51        ImmutableClassesGiraphConfiguration conf) {
52      this.minLocalEdgesRatio = conf.getFloat(
53          PseudoRandomInputFormatConstants.LOCAL_EDGES_MIN_RATIO,
54          PseudoRandomInputFormatConstants.LOCAL_EDGES_MIN_RATIO_DEFAULT);
55      this.numVertices = numVertices;
56      int numWorkers = conf.getMaxWorkers();
57      List<WorkerInfo> workerInfos = Collections.nCopies(numWorkers,
58          new WorkerInfo());
59      numPartitions = PartitionUtils.computePartitionCount(
60          workerInfos.size(), conf);
61      partitionSize = numVertices / numPartitions;
62    }
63  
64    /**
65     * Generate a destination vertex id for the given source vertex,
66     * using the desired configuration for edge locality and the provided
67     * pseudo-random generator.
68     *
69     * @param sourceVertexId Source vertex id.
70     * @param rand           Pseudo-random generator.
71     * @return Destination vertex id.
72     */
73    public int generateDestVertex(int sourceVertexId, Random rand) {
74      if (rand.nextFloat() < minLocalEdgesRatio) {
75        int partitionId = sourceVertexId % numPartitions;
76        return partitionId + numPartitions * rand.nextInt(partitionSize);
77      } else {
78        return rand.nextInt(numVertices);
79      }
80    }
81  }