/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /* * This file is available under and governed by the GNU General Public * License version 2 only, as published by the Free Software Foundation. * However, the following notice accompanied the original version of this * file: * * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/1.0/ */ package java.util.concurrent; import java.util.Random; /** * A random number generator isolated to the current thread. Like the * global {@link java.util.Random} generator used by the {@link * java.lang.Math} class, a {@code ThreadLocalRandom} is initialized * with an internally generated seed that may not otherwise be * modified. When applicable, use of {@code ThreadLocalRandom} rather * than shared {@code Random} objects in concurrent programs will * typically encounter much less overhead and contention. Use of * {@code ThreadLocalRandom} is particularly appropriate when multiple * tasks (for example, each a {@link ForkJoinTask}) use random numbers * in parallel in thread pools. * *
Usages of this class should typically be of the form: * {@code ThreadLocalRandom.current().nextX(...)} (where * {@code X} is {@code Int}, {@code Long}, etc). * When all usages are of this form, it is never possible to * accidently share a {@code ThreadLocalRandom} across multiple threads. * *
This class also provides additional commonly used bounded random
* generation methods.
*
* @since 1.7
* @author Doug Lea
*/
public class ThreadLocalRandom extends Random {
// same constants as Random, but must be redeclared because private
private static final long multiplier = 0x5DEECE66DL;
private static final long addend = 0xBL;
private static final long mask = (1L << 48) - 1;
/**
* The random seed. We can't use super.seed.
*/
private long rnd;
/**
* Initialization flag to permit calls to setSeed to succeed only
* while executing the Random constructor. We can't allow others
* since it would cause setting seed in one part of a program to
* unintentionally impact other usages by the thread.
*/
boolean initialized;
// Padding to help avoid memory contention among seed updates in
// different TLRs in the common case that they are located near
// each other.
private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
/**
* The actual ThreadLocal
*/
private static final ThreadLocal