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,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.apache.myfaces.util;
20
21 import java.util.Random;
22
23 /**
24 * A threadsafe implementation of {@link XorShiftRandom}.
25 * We use a ThreadLocal to give each thread it's own implementation.
26 */
27 public class ThreadsafeXorShiftRandom extends XorShiftRandom
28 {
29 /**
30 * Only used for creating the initial seed for each thread!
31 *
32 * We use a threadsafe java.util.Random for making sure that
33 * each thread get it's very own initial seed value.
34 *
35 * If we would not do this then starting dozen Threads at the same time
36 * would result in all having the same seed and thus generate
37 * the same random numbers.
38 */
39 private static Random seedRandom = new Random(System.nanoTime());
40
41 public ThreadsafeXorShiftRandom()
42 {
43 // seed is not used but created by the ThreadLocal
44 super(0);
45 }
46
47 private static final ThreadLocal<XorShiftRandom> randomThreadLocal = new ThreadLocal<XorShiftRandom>()
48 {
49 @Override
50 protected XorShiftRandom initialValue()
51 {
52 return new XorShiftRandom(seedRandom.nextLong());
53 }
54 };
55
56 /**
57 * We use the random generator for this very thread.
58 * This method is perfectly threadsafe. It is also guaranteed
59 * that each thread will get own values.
60 */
61 @Override
62 public long random()
63 {
64 return randomThreadLocal.get().random();
65 }
66 }