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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.writable.kryo;
19  
20  import java.util.Random;
21  
22  /**
23   * Transient Random class. Seed/state is not kept after
24   * serializing/deserializing.
25   *
26   * Within Blocks Framework - if we initialize Random within the Piece, when
27   * it's serialzied and copied to all workers and all threads - keeping seed
28   * would cause same series of random numbers to be generated everywhere.
29   *
30   * So this class is safe to be used in Pieces, while using regular Random
31   * class is forbidden to be serialized.
32   * Best approach would be to not have Random serialized, and create it on
33   * workers, where possible.
34   */
35  public class TransientRandom {
36    /** Instance of random object */
37    private final transient Random random = new Random();
38  
39    /**
40     * Get instance of Random
41     * @return Random instance
42     */
43    public Random get() {
44      return random;
45    }
46  
47    /**
48     * Returns a pseudorandom, uniformly distributed {@code int} value
49     * between 0 (inclusive) and the specified value (exclusive), drawn from
50     * this random number generator's sequence.
51     *
52     * @param n Given upper limit
53     * @return pseudorandom integer number in [0, n) range.
54     */
55    public int nextInt(int n) {
56      return random.nextInt(n);
57    }
58  
59    /**
60     * Returns the next pseudorandom, uniformly distributed
61     * {@code double} value between {@code 0.0} and
62     * {@code 1.0} from this random number generator's sequence.
63     *
64     * @return pseudorandom number in [0, 1)
65     */
66    public double nextDouble() {
67      return random.nextDouble();
68    }
69  }