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Revision **1.2** -
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*Fri Jul 19 19:34:43 2013 UTC*
(4 years, 7 months ago)
by *jsr166*

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Changes since**1.1: +1 -1 lines**

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/* * 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 jsr166e; 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. * * <p>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. * * <p>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<ThreadLocalRandom> localRandom = new ThreadLocal<ThreadLocalRandom>() { protected ThreadLocalRandom initialValue() { return new ThreadLocalRandom(); } }; /** * Constructor called only by localRandom.initialValue. */ ThreadLocalRandom() { super(); initialized = true; } /** * 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) * @return the next value * @throws IllegalArgumentException if least greater than or equal * to bound */ 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; }

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