ThreadLocalRandom.java

package com.alibaba.jstorm.common.metric.codahale;

import java.util.Random;

/**
 * @author wange
 * @since 15/12/16
 */
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) {
            final int bits = next(2);
            final long half = n >>> 1;
            final 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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