com.alibaba.middleware.ushura.util.ThreadLocalRandom Maven / Gradle / Ivy
/*
* Copyright 2013 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/publicdomain/zero/1.0/
*/
package com.alibaba.middleware.ushura.util;
import java.security.SecureRandom;
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
* 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 io.netty.util.internal.chmv8.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
*/
@SuppressWarnings("all")
public class ThreadLocalRandom extends Random {
private static final AtomicLong seedUniquifier = new AtomicLong();
private static volatile long initialSeedUniquifier;
public static void setInitialSeedUniquifier(long initialSeedUniquifier) {
ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
}
public static synchronized long getInitialSeedUniquifier() {
// Use the value set via the setter.
long initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
// Otherwise, generate one.
if (initialSeedUniquifier == 0) {
// Try to generate a real random number from /dev/random.
// Get from a different thread to avoid blocking indefinitely on a machine without much entrophy.
final BlockingQueue queue = new LinkedBlockingQueue();
Thread generatorThread = new Thread("initialSeedUniquifierGenerator") {
@Override
public void run() {
SecureRandom random = new SecureRandom(); // Get the real random seed from /dev/random
queue.add(random.nextLong());
}
};
generatorThread.start();
// Get the random seed from the thread with timeout.
final long timeoutSeconds = 3;
final long deadLine = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds);
for (;;) {
long waitTime = deadLine - System.nanoTime();
if (waitTime <= 0) {
break;
}
try {
Long result = queue.poll(waitTime, TimeUnit.NANOSECONDS);
if (result != null) {
initialSeedUniquifier = result;
break;
}
} catch (InterruptedException ignore) {
// Ignore
}
}
// Just in case the initialSeedUniquifier is zero or some other constant
initialSeedUniquifier ^= 0x3255ecdc33bae119L; // just a meaningless random number
initialSeedUniquifier ^= Long.reverse(System.nanoTime());
ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
}
return initialSeedUniquifier;
}
private static long newSeed() {
for (;;) {
final long current = seedUniquifier.get();
final long actualCurrent = current != 0 ? current : getInitialSeedUniquifier();
// L'Ecuyer, "Tables of Linear Congruential Generators of Different Sizes and Good Lattice Structure", 1999
final long next = actualCurrent * 181783497276652981L;
if (seedUniquifier.compareAndSet(current, next)) {
return next ^ System.nanoTime();
}
}
}
// 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;
/**
* Constructor called only by localRandom.initialValue.
*/
ThreadLocalRandom() {
super(newSeed());
initialized = true;
}
/**
* The actual ThreadLocal
*/
private static final ThreadLocal localRandom = new ThreadLocal() {
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
*/
public void setSeed(long seed) {
if (initialized) {
throw new UnsupportedOperationException();
}
rnd = (seed ^ multiplier) & mask;
}
protected int next(int bits) {
rnd = (rnd * multiplier + addend) & mask;
return (int) (rnd >>> (48 - bits));
}
/**
* Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound
* (exclusive).
*
* @param least
* the least value returned
* @param bound
* the upper bound (exclusive)
* @throws IllegalArgumentException
* if least greater than or equal to bound
* @return the next value
*/
public int nextInt(int least, int bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextInt(bound - least) + least;
}
/**
* Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).
*
* @param n
* the bound on the random number to be returned. Must be positive.
* @return the next value
* @throws IllegalArgumentException
* if n is not positive
*/
public long nextLong(long n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be positive");
}
// Divide n by two until small enough for nextInt. On each
// iteration (at most 31 of them but usually much less),
// randomly choose both whether to include high bit in result
// (offset) and whether to continue with the lower vs upper
// half (which makes a difference only if odd).
long offset = 0;
while (n >= Integer.MAX_VALUE) {
int bits = next(2);
long half = n >>> 1;
long nextn = ((bits & 2) == 0) ? half : n - half;
if ((bits & 1) == 0) {
offset += n - nextn;
}
n = nextn;
}
return offset + nextInt((int) n);
}
/**
* Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound
* (exclusive).
*
* @param least
* the least value returned
* @param bound
* the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException
* if least greater than or equal to bound
*/
public long nextLong(long least, long bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextLong(bound - least) + least;
}
/**
* Returns a pseudorandom, uniformly distributed {@code double} value between 0 (inclusive) and the specified value
* (exclusive).
*
* @param n
* the bound on the random number to be returned. Must be positive.
* @return the next value
* @throws IllegalArgumentException
* if n is not positive
*/
public double nextDouble(double n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be positive");
}
return nextDouble() * n;
}
/**
* Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound
* (exclusive).
*
* @param least
* the least value returned
* @param bound
* the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException
* if least greater than or equal to bound
*/
public double nextDouble(double least, double bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextDouble() * (bound - least) + least;
}
private static final long serialVersionUID = -5851777807851030925L;
}