/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * 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 java.util.concurrent;

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

    /**

     * 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)

     * @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;

}