001/*
002 * Copyright 2014 UnboundID Corp.
003 * All Rights Reserved.
004 */
005/*
006 * Copyright (C) 2014 UnboundID Corp.
007 *
008 * This program is free software; you can redistribute it and/or modify
009 * it under the terms of the GNU General Public License (GPLv2 only)
010 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
011 * as published by the Free Software Foundation.
012 *
013 * This program is distributed in the hope that it will be useful,
014 * but WITHOUT ANY WARRANTY; without even the implied warranty of
015 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
016 * GNU General Public License for more details.
017 *
018 * You should have received a copy of the GNU General Public License
019 * along with this program; if not, see <http://www.gnu.org/licenses>.
020 */
021package com.unboundid.util;
022
023
024
025import java.util.Random;
026
027
028
029/**
030 * This class provides a means of obtaining a thread-local random number
031 * generator that can be used by the current thread without the need for
032 * synchronization.
033 */
034@ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
035public final class ThreadLocalRandom
036{
037  /**
038   * The random number generator that will be used to seed per-thread instances.
039   */
040  private static final Random SEED_RANDOM = new Random();
041
042
043
044  /**
045   * The thread-local instances that have been created.
046   */
047  private static final ThreadLocal<Random> INSTANCES =
048       new ThreadLocal<Random>();
049
050
051
052  /**
053   * Prevents this class from being instantiated.
054   */
055  private ThreadLocalRandom()
056  {
057    // No implementation required.
058  }
059
060
061
062  /**
063   * Gets a thread-local random number generator instance.
064   *
065   * @return  A thread-local random number generator instance.
066   */
067  public static Random get()
068  {
069    Random r = INSTANCES.get();
070    if (r == null)
071    {
072      final long seed;
073      synchronized (SEED_RANDOM)
074      {
075        seed = SEED_RANDOM.nextLong();
076      }
077
078      r = new Random(seed);
079      INSTANCES.set(r);
080    }
081
082    return r;
083  }
084}