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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 | +} | |