/*

  * Licensed to the Apache Software Foundation (ASF) under one

  * or more contributor license agreements.  See the NOTICE file

  * distributed with this work for additional information

  * regarding copyright ownership.  The ASF licenses this file

  * to you under the Apache License, Version 2.0 (the

  * "License"); you may not use this file except in compliance

  * with the License.  You may obtain a copy of the License at

  *

  *   http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing,

  * software distributed under the License is distributed on an

  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

  * KIND, either express or implied.  See the License for the

  * specific language governing permissions and limitations

  * under the License.

  */

 package org.apache.myfaces.util;

 import java.util.Random;

 /**

  * A threadsafe implementation of {@link XorShiftRandom}.

  * We use a ThreadLocal to give each thread it's own implementation.

  */

 public class ThreadsafeXorShiftRandom extends XorShiftRandom

 {

     /**

      * Only used for creating the initial seed for each thread!

      *

      * We use a threadsafe java.util.Random for making sure that

      * each thread get it's very own initial seed value.

      *

      * If we would not do this then starting dozen Threads at the same time

      * would result in all having the same seed and thus generate

      * the same random numbers.

      */

     private static Random seedRandom = new Random(System.nanoTime());

     public ThreadsafeXorShiftRandom()

     {

         // seed is not used but created by the ThreadLocal

         super(0);

     }

     private static final ThreadLocal<XorShiftRandom> randomThreadLocal = new ThreadLocal<XorShiftRandom>()

     {

         @Override

         protected XorShiftRandom initialValue()

         {

             return new XorShiftRandom(seedRandom.nextLong());

         }

     };

     /**

      * We use the random generator for this very thread.

      * This method is perfectly threadsafe. It is also guaranteed

      * that each thread will get own values.

      */

     @Override

     public long random()

     {

         return randomThreadLocal.get().random();

     }

 }