/*
* 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 jsr166y;
import java.util.*;
/**
* A Random number generator with the same properties as {@link
* Random} but isolated to the current Thread. Like the global
* generator used by {@link java.lang.Math}, a ThreadLocalRandom is
* initialized with an internally generated seed that may not
* otherwise be modified. When applicable, use of ThreadLocalRandom
* rather than shared Random objects in concurrent programs will
* typically encounter less overhead and contention. The most common
* usage form is: ThreadLocalRandom.current().nextX()
.
*
*
This class also provides additional commonly used bounded random
* generation methods.
*/
public class ThreadLocalRandom extends Random {
// same constants as Random, but must be redeclared because private
private final static long multiplier = 0x5DEECE66DL;
private final static long addend = 0xBL;
private final static 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 inintentionally 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;
private static final ThreadLocal localRandom =
new ThreadLocal() {
protected ThreadLocalRandom initialValue() {
return new ThreadLocalRandom();
}
};
ThreadLocalRandom() { // construct only in localRandom.initialValue
super(); // super constructor calls setSeed
}
/**
* Returns the current Thread's ThreadLocalRandom
* @return the current Thread's ThreadLocalRandom
*/
public static ThreadLocalRandom current() {
return localRandom.get();
}
/**
* Throws UnsupportedOperationException. Setting seeds in this
* generator is unsupported.
* @throw UnsupportedOperationException always
*/
public void setSeed(long seed) {
if (initialized)
throw new UnsupportedOperationException();
initialized = true;
rnd = (seed ^ multiplier) & mask;
}
protected int next(int bits) {
return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (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");
long offset = 0;
while (n >= Integer.MAX_VALUE) { // randomly pick half range
int bits = next(2); // 2nd bit for odd vs even split
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;
}
}