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/*
* Copyright 2012 The Netty Project
*
* The Netty Project 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.
*/
/*
* 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/licenses/publicdomain
*/
package org.jboss.netty.util.internal;
import java.util.Random;
/**
* A random number generator isolated to the current thread. Like the
* global {@link Random} generator used by the {@link
* 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 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
*/
public final 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 the first and only allowed call
* to setSeed (inside Random constructor) to succeed. 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.
*/
private 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.
@SuppressWarnings("unused")
private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
/**
* The actual ThreadLocal
*/
private static final ThreadLocal localRandom =
new ThreadLocal() {
@Override
protected ThreadLocalRandom initialValue() {
return new ThreadLocalRandom();
}
};
/**
* Returns the current thread's {@code ThreadLocalRandom}.
*
* @return the current thread's {@code ThreadLocalRandom}
*/
public static ThreadLocalRandom current() {
return localRandom.get();
}
/**
* Throws {@code UnsupportedOperationException}. Setting seeds in
* this generator is not supported.
*
* @throws UnsupportedOperationException always
*/
@Override
public void setSeed(long seed) {
// We rely on the fact that the superclass no-arg constructor
// invokes setSeed exactly once to initialize.
if (initialized) {
throw new UnsupportedOperationException();
}
initialized = true;
rnd = (seed ^ multiplier) & mask;
}
@Override
protected int next(int bits) {
rnd = rnd * multiplier + addend & mask;
return (int) (rnd >>> 48 - bits);
}
private static final long serialVersionUID = -5851777807851030925L;
}