jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent;
jaroslav@1890: 
jaroslav@1890: import java.util.Random;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * A random number generator isolated to the current thread.  Like the
jaroslav@1890:  * global {@link java.util.Random} generator used by the {@link
jaroslav@1890:  * java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
jaroslav@1890:  * with an internally generated seed that may not otherwise be
jaroslav@1890:  * modified. When applicable, use of {@code ThreadLocalRandom} rather
jaroslav@1890:  * than shared {@code Random} objects in concurrent programs will
jaroslav@1890:  * typically encounter much less overhead and contention.  Use of
jaroslav@1890:  * {@code ThreadLocalRandom} is particularly appropriate when multiple
jaroslav@1890:  * tasks (for example, each a {@link ForkJoinTask}) use random numbers
jaroslav@1890:  * in parallel in thread pools.
jaroslav@1890:  *
jaroslav@1890:  * <p>Usages of this class should typically be of the form:
jaroslav@1890:  * {@code ThreadLocalRandom.current().nextX(...)} (where
jaroslav@1890:  * {@code X} is {@code Int}, {@code Long}, etc).
jaroslav@1890:  * When all usages are of this form, it is never possible to
jaroslav@1890:  * accidently share a {@code ThreadLocalRandom} across multiple threads.
jaroslav@1890:  *
jaroslav@1890:  * <p>This class also provides additional commonly used bounded random
jaroslav@1890:  * generation methods.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.7
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  */
jaroslav@1890: public class ThreadLocalRandom extends Random {
jaroslav@1890:     // same constants as Random, but must be redeclared because private
jaroslav@1890:     private static final long multiplier = 0x5DEECE66DL;
jaroslav@1890:     private static final long addend = 0xBL;
jaroslav@1890:     private static final long mask = (1L << 48) - 1;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The random seed. We can't use super.seed.
jaroslav@1890:      */
jaroslav@1890:     private long rnd;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Initialization flag to permit calls to setSeed to succeed only
jaroslav@1890:      * while executing the Random constructor.  We can't allow others
jaroslav@1890:      * since it would cause setting seed in one part of a program to
jaroslav@1890:      * unintentionally impact other usages by the thread.
jaroslav@1890:      */
jaroslav@1890:     boolean initialized;
jaroslav@1890: 
jaroslav@1890:     // Padding to help avoid memory contention among seed updates in
jaroslav@1890:     // different TLRs in the common case that they are located near
jaroslav@1890:     // each other.
jaroslav@1890:     private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The actual ThreadLocal
jaroslav@1890:      */
jaroslav@1890:     private static final ThreadLocal<ThreadLocalRandom> localRandom =
jaroslav@1890:         new ThreadLocal<ThreadLocalRandom>() {
jaroslav@1890:             protected ThreadLocalRandom initialValue() {
jaroslav@1890:                 return new ThreadLocalRandom();
jaroslav@1890:             }
jaroslav@1890:     };
jaroslav@1890: 
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Constructor called only by localRandom.initialValue.
jaroslav@1890:      */
jaroslav@1890:     ThreadLocalRandom() {
jaroslav@1890:         super();
jaroslav@1890:         initialized = true;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the current thread's {@code ThreadLocalRandom}.
jaroslav@1890:      *
jaroslav@1890:      * @return the current thread's {@code ThreadLocalRandom}
jaroslav@1890:      */
jaroslav@1890:     public static ThreadLocalRandom current() {
jaroslav@1890:         return localRandom.get();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Throws {@code UnsupportedOperationException}.  Setting seeds in
jaroslav@1890:      * this generator is not supported.
jaroslav@1890:      *
jaroslav@1890:      * @throws UnsupportedOperationException always
jaroslav@1890:      */
jaroslav@1890:     public void setSeed(long seed) {
jaroslav@1890:         if (initialized)
jaroslav@1890:             throw new UnsupportedOperationException();
jaroslav@1890:         rnd = (seed ^ multiplier) & mask;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     protected int next(int bits) {
jaroslav@1890:         rnd = (rnd * multiplier + addend) & mask;
jaroslav@1890:         return (int) (rnd >>> (48-bits));
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a pseudorandom, uniformly distributed value between the
jaroslav@1890:      * given least value (inclusive) and bound (exclusive).
jaroslav@1890:      *
jaroslav@1890:      * @param least the least value returned
jaroslav@1890:      * @param bound the upper bound (exclusive)
jaroslav@1890:      * @throws IllegalArgumentException if least greater than or equal
jaroslav@1890:      * to bound
jaroslav@1890:      * @return the next value
jaroslav@1890:      */
jaroslav@1890:     public int nextInt(int least, int bound) {
jaroslav@1890:         if (least >= bound)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         return nextInt(bound - least) + least;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a pseudorandom, uniformly distributed value
jaroslav@1890:      * between 0 (inclusive) and the specified value (exclusive).
jaroslav@1890:      *
jaroslav@1890:      * @param n the bound on the random number to be returned.  Must be
jaroslav@1890:      *        positive.
jaroslav@1890:      * @return the next value
jaroslav@1890:      * @throws IllegalArgumentException if n is not positive
jaroslav@1890:      */
jaroslav@1890:     public long nextLong(long n) {
jaroslav@1890:         if (n <= 0)
jaroslav@1890:             throw new IllegalArgumentException("n must be positive");
jaroslav@1890:         // Divide n by two until small enough for nextInt. On each
jaroslav@1890:         // iteration (at most 31 of them but usually much less),
jaroslav@1890:         // randomly choose both whether to include high bit in result
jaroslav@1890:         // (offset) and whether to continue with the lower vs upper
jaroslav@1890:         // half (which makes a difference only if odd).
jaroslav@1890:         long offset = 0;
jaroslav@1890:         while (n >= Integer.MAX_VALUE) {
jaroslav@1890:             int bits = next(2);
jaroslav@1890:             long half = n >>> 1;
jaroslav@1890:             long nextn = ((bits & 2) == 0) ? half : n - half;
jaroslav@1890:             if ((bits & 1) == 0)
jaroslav@1890:                 offset += n - nextn;
jaroslav@1890:             n = nextn;
jaroslav@1890:         }
jaroslav@1890:         return offset + nextInt((int) n);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a pseudorandom, uniformly distributed value between the
jaroslav@1890:      * given least value (inclusive) and bound (exclusive).
jaroslav@1890:      *
jaroslav@1890:      * @param least the least value returned
jaroslav@1890:      * @param bound the upper bound (exclusive)
jaroslav@1890:      * @return the next value
jaroslav@1890:      * @throws IllegalArgumentException if least greater than or equal
jaroslav@1890:      * to bound
jaroslav@1890:      */
jaroslav@1890:     public long nextLong(long least, long bound) {
jaroslav@1890:         if (least >= bound)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         return nextLong(bound - least) + least;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a pseudorandom, uniformly distributed {@code double} value
jaroslav@1890:      * between 0 (inclusive) and the specified value (exclusive).
jaroslav@1890:      *
jaroslav@1890:      * @param n the bound on the random number to be returned.  Must be
jaroslav@1890:      *        positive.
jaroslav@1890:      * @return the next value
jaroslav@1890:      * @throws IllegalArgumentException if n is not positive
jaroslav@1890:      */
jaroslav@1890:     public double nextDouble(double n) {
jaroslav@1890:         if (n <= 0)
jaroslav@1890:             throw new IllegalArgumentException("n must be positive");
jaroslav@1890:         return nextDouble() * n;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a pseudorandom, uniformly distributed value between the
jaroslav@1890:      * given least value (inclusive) and bound (exclusive).
jaroslav@1890:      *
jaroslav@1890:      * @param least the least value returned
jaroslav@1890:      * @param bound the upper bound (exclusive)
jaroslav@1890:      * @return the next value
jaroslav@1890:      * @throws IllegalArgumentException if least greater than or equal
jaroslav@1890:      * to bound
jaroslav@1890:      */
jaroslav@1890:     public double nextDouble(double least, double bound) {
jaroslav@1890:         if (least >= bound)
jaroslav@1890:             throw new IllegalArgumentException();
jaroslav@1890:         return nextDouble() * (bound - least) + least;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     private static final long serialVersionUID = -5851777807851030925L;
jaroslav@1890: }