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| 1 | /* | ||
| 2 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 3 | * | ||
| 4 | * This code is free software; you can redistribute it and/or modify it | ||
| 5 | * under the terms of the GNU General Public License version 2 only, as | ||
| 6 | * published by the Free Software Foundation. Oracle designates this | ||
| 7 | * particular file as subject to the "Classpath" exception as provided | ||
| 8 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 9 | * | ||
| 10 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 11 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 12 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 13 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 14 | * accompanied this code). | ||
| 15 | * | ||
| 16 | * You should have received a copy of the GNU General Public License version | ||
| 17 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 18 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 19 | * | ||
| 20 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 21 | * or visit www.oracle.com if you need additional information or have any | ||
| 22 | * questions. | ||
| 23 | */ | ||
| 24 | |||
| 25 | /* | ||
| 26 | * This file is available under and governed by the GNU General Public | ||
| 27 | * License version 2 only, as published by the Free Software Foundation. | ||
| 28 | * However, the following notice accompanied the original version of this | ||
| 29 | * file: | ||
| 30 | * | ||
| 31 | * Written by Doug Lea with assistance from members of JCP JSR-166 | ||
| 32 | * Expert Group and released to the public domain, as explained at | ||
| 33 | * http://creativecommons.org/publicdomain/zero/1.0/ | ||
| 34 | */ | ||
| 35 | |||
| 36 | package java.util.concurrent; | ||
| 37 | |||
| 38 | import java.util.Random; | ||
| 39 | |||
| 40 | /** | ||
| 41 | * A random number generator isolated to the current thread. Like the | ||
| 42 | * global {@link java.util.Random} generator used by the {@link | ||
| 43 | * java.lang.Math} class, a {@code ThreadLocalRandom} is initialized | ||
| 44 | * with an internally generated seed that may not otherwise be | ||
| 45 | * modified. When applicable, use of {@code ThreadLocalRandom} rather | ||
| 46 | * than shared {@code Random} objects in concurrent programs will | ||
| 47 | * typically encounter much less overhead and contention. Use of | ||
| 48 | * {@code ThreadLocalRandom} is particularly appropriate when multiple | ||
| 49 | * tasks (for example, each a {@link ForkJoinTask}) use random numbers | ||
| 50 | * in parallel in thread pools. | ||
| 51 | * | ||
| 52 | * <p>Usages of this class should typically be of the form: | ||
| 53 | * {@code ThreadLocalRandom.current().nextX(...)} (where | ||
| 54 | * {@code X} is {@code Int}, {@code Long}, etc). | ||
| 55 | * When all usages are of this form, it is never possible to | ||
| 56 | * accidently share a {@code ThreadLocalRandom} across multiple threads. | ||
| 57 | * | ||
| 58 | * <p>This class also provides additional commonly used bounded random | ||
| 59 | * generation methods. | ||
| 60 | * | ||
| 61 | * @since 1.7 | ||
| 62 | * @author Doug Lea | ||
| 63 | */ | ||
| 64 | public class ThreadLocalRandom extends Random { | ||
| 65 | // same constants as Random, but must be redeclared because private | ||
| 66 | private static final long multiplier = 0x5DEECE66DL; | ||
| 67 | private static final long addend = 0xBL; | ||
| 68 | private static final long mask = (1L << 48) - 1; | ||
| 69 | |||
| 70 | /** | ||
| 71 | * The random seed. We can't use super.seed. | ||
| 72 | */ | ||
| 73 | private long rnd; | ||
| 74 | |||
| 75 | /** | ||
| 76 | * Initialization flag to permit calls to setSeed to succeed only | ||
| 77 | * while executing the Random constructor. We can't allow others | ||
| 78 | * since it would cause setting seed in one part of a program to | ||
| 79 | * unintentionally impact other usages by the thread. | ||
| 80 | */ | ||
| 81 | boolean initialized; | ||
| 82 | |||
| 83 | // Padding to help avoid memory contention among seed updates in | ||
| 84 | // different TLRs in the common case that they are located near | ||
| 85 | // each other. | ||
| 86 | private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7; | ||
| 87 | |||
| 88 | /** | ||
| 89 | * The actual ThreadLocal | ||
| 90 | */ | ||
| 91 | private static final ThreadLocal<ThreadLocalRandom> localRandom = | ||
| 92 | new ThreadLocal<ThreadLocalRandom>() { | ||
| 93 | protected ThreadLocalRandom initialValue() { | ||
| 94 | return new ThreadLocalRandom(); | ||
| 95 | } | ||
| 96 | }; | ||
| 97 | |||
| 98 | |||
| 99 | /** | ||
| 100 | * Constructor called only by localRandom.initialValue. | ||
| 101 | */ | ||
| 102 | ThreadLocalRandom() { | ||
| 103 | super(); | ||
| 104 | initialized = true; | ||
| 105 | } | ||
| 106 | |||
| 107 | /** | ||
| 108 | * Returns the current thread's {@code ThreadLocalRandom}. | ||
| 109 | * | ||
| 110 | * @return the current thread's {@code ThreadLocalRandom} | ||
| 111 | */ | ||
| 112 | public static ThreadLocalRandom current() { | ||
| 113 | return localRandom.get(); | ||
| 114 | } | ||
| 115 | |||
| 116 | /** | ||
| 117 | * Throws {@code UnsupportedOperationException}. Setting seeds in | ||
| 118 | * this generator is not supported. | ||
| 119 | * | ||
| 120 | * @throws UnsupportedOperationException always | ||
| 121 | */ | ||
| 122 | public void setSeed(long seed) { | ||
| 123 | if (initialized) | ||
| 124 | throw new UnsupportedOperationException(); | ||
| 125 | rnd = (seed ^ multiplier) & mask; | ||
| 126 | } | ||
| 127 | |||
| 128 | protected int next(int bits) { | ||
| 129 | rnd = (rnd * multiplier + addend) & mask; | ||
| 130 | return (int) (rnd >>> (48-bits)); | ||
| 131 | } | ||
| 132 | |||
| 133 | /** | ||
| 134 | * Returns a pseudorandom, uniformly distributed value between the | ||
| 135 | * given least value (inclusive) and bound (exclusive). | ||
| 136 | * | ||
| 137 | * @param least the least value returned | ||
| 138 | * @param bound the upper bound (exclusive) | ||
| 139 | * @throws IllegalArgumentException if least greater than or equal | ||
| 140 | * to bound | ||
| 141 | * @return the next value | ||
| 142 | */ | ||
| 143 | public int nextInt(int least, int bound) { | ||
| 144 | if (least >= bound) | ||
| 145 | throw new IllegalArgumentException(); | ||
| 146 | return nextInt(bound - least) + least; | ||
| 147 | } | ||
| 148 | |||
| 149 | /** | ||
| 150 | * Returns a pseudorandom, uniformly distributed value | ||
| 151 | * between 0 (inclusive) and the specified value (exclusive). | ||
| 152 | * | ||
| 153 | * @param n the bound on the random number to be returned. Must be | ||
| 154 | * positive. | ||
| 155 | * @return the next value | ||
| 156 | * @throws IllegalArgumentException if n is not positive | ||
| 157 | */ | ||
| 158 | public long nextLong(long n) { | ||
| 159 | if (n <= 0) | ||
| 160 | throw new IllegalArgumentException("n must be positive"); | ||
| 161 | // Divide n by two until small enough for nextInt. On each | ||
| 162 | // iteration (at most 31 of them but usually much less), | ||
| 163 | // randomly choose both whether to include high bit in result | ||
| 164 | // (offset) and whether to continue with the lower vs upper | ||
| 165 | // half (which makes a difference only if odd). | ||
| 166 | long offset = 0; | ||
| 167 | while (n >= Integer.MAX_VALUE) { | ||
| 168 | int bits = next(2); | ||
| 169 | long half = n >>> 1; | ||
| 170 | long nextn = ((bits & 2) == 0) ? half : n - half; | ||
| 171 | if ((bits & 1) == 0) | ||
| 172 | offset += n - nextn; | ||
| 173 | n = nextn; | ||
| 174 | } | ||
| 175 | return offset + nextInt((int) n); | ||
| 176 | } | ||
| 177 | |||
| 178 | /** | ||
| 179 | * Returns a pseudorandom, uniformly distributed value between the | ||
| 180 | * given least value (inclusive) and bound (exclusive). | ||
| 181 | * | ||
| 182 | * @param least the least value returned | ||
| 183 | * @param bound the upper bound (exclusive) | ||
| 184 | * @return the next value | ||
| 185 | * @throws IllegalArgumentException if least greater than or equal | ||
| 186 | * to bound | ||
| 187 | */ | ||
| 188 | public long nextLong(long least, long bound) { | ||
| 189 | if (least >= bound) | ||
| 190 | throw new IllegalArgumentException(); | ||
| 191 | return nextLong(bound - least) + least; | ||
| 192 | } | ||
| 193 | |||
| 194 | /** | ||
| 195 | * Returns a pseudorandom, uniformly distributed {@code double} value | ||
| 196 | * between 0 (inclusive) and the specified value (exclusive). | ||
| 197 | * | ||
| 198 | * @param n the bound on the random number to be returned. Must be | ||
| 199 | * positive. | ||
| 200 | * @return the next value | ||
| 201 | * @throws IllegalArgumentException if n is not positive | ||
| 202 | */ | ||
| 203 | public double nextDouble(double n) { | ||
| 204 | if (n <= 0) | ||
| 205 | throw new IllegalArgumentException("n must be positive"); | ||
| 206 | return nextDouble() * n; | ||
| 207 | } | ||
| 208 | |||
| 209 | /** | ||
| 210 | * Returns a pseudorandom, uniformly distributed value between the | ||
| 211 | * given least value (inclusive) and bound (exclusive). | ||
| 212 | * | ||
| 213 | * @param least the least value returned | ||
| 214 | * @param bound the upper bound (exclusive) | ||
| 215 | * @return the next value | ||
| 216 | * @throws IllegalArgumentException if least greater than or equal | ||
| 217 | * to bound | ||
| 218 | */ | ||
| 219 | public double nextDouble(double least, double bound) { | ||
| 220 | if (least >= bound) | ||
| 221 | throw new IllegalArgumentException(); | ||
| 222 | return nextDouble() * (bound - least) + least; | ||
| 223 | } | ||
| 224 | |||
| 225 | private static final long serialVersionUID = -5851777807851030925L; | ||
| 226 | } | ||