| /* |
| * 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/publicdomain/zero/1.0/ |
| * |
| * Additional modifications by Guy Steele in 2019 to refactor the code |
| * and to implement the {@link RandomGenerator} interface. |
| */ |
| |
| package java.util.concurrent; |
| |
| import java.io.ObjectStreamField; |
| import java.math.BigInteger; |
| import java.security.AccessControlContext; |
| import java.util.Map; |
| import java.util.Random; |
| import java.util.Spliterator; |
| import java.util.concurrent.atomic.AtomicInteger; |
| import java.util.concurrent.atomic.AtomicLong; |
| import java.util.random.RandomGenerator; |
| import java.util.stream.DoubleStream; |
| import java.util.stream.IntStream; |
| import java.util.stream.LongStream; |
| import jdk.internal.util.random.RandomSupport; |
| import jdk.internal.util.random.RandomSupport.*; |
| import jdk.internal.misc.Unsafe; |
| import jdk.internal.misc.VM; |
| |
| /** |
| * A random number generator (with period 2<sup>64</sup>) 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 |
| * accidentally share a {@code ThreadLocalRandom} across multiple threads. |
| * |
| * <p>This class also provides additional commonly used bounded random |
| * generation methods. |
| * |
| * <p>Instances of {@code ThreadLocalRandom} are not cryptographically |
| * secure. Consider instead using {@link java.security.SecureRandom} |
| * in security-sensitive applications. Additionally, |
| * default-constructed instances do not use a cryptographically random |
| * seed unless the {@linkplain System#getProperty system property} |
| * {@code java.util.secureRandomSeed} is set to {@code true}. |
| * |
| * @since 1.7 |
| * @author Doug Lea |
| */ |
| |
| @RandomGeneratorProperties( |
| name = "ThreadLocalRandom", |
| i = 64, j = 0, k = 0, |
| equidistribution = 1 |
| ) |
| public class ThreadLocalRandom extends Random { |
| /* |
| * This class implements the java.util.Random API (and subclasses |
| * Random) using a single static instance that accesses 64 bits of |
| * random number state held in class java.lang.Thread (field |
| * threadLocalRandomSeed). In doing so, it also provides a home |
| * for managing package-private utilities that rely on exactly the |
| * same state as needed to maintain the ThreadLocalRandom |
| * instances. We leverage the need for an initialization flag |
| * field to also use it as a "probe" -- a self-adjusting thread |
| * hash used for contention avoidance, as well as a secondary |
| * simpler (xorShift) random seed that is conservatively used to |
| * avoid otherwise surprising users by hijacking the |
| * ThreadLocalRandom sequence. The dual use is a marriage of |
| * convenience, but is a simple and efficient way of reducing |
| * application-level overhead and footprint of most concurrent |
| * programs. Even more opportunistically, we also define here |
| * other package-private utilities that access Thread class |
| * fields. |
| * |
| * Even though this class subclasses java.util.Random, it uses the |
| * same basic algorithm as java.util.SplittableRandom. (See its |
| * internal documentation for explanations, which are not repeated |
| * here.) Note that ThreadLocalRandom is not a "splittable" generator |
| * (it does not support the split method), but it behaves as if |
| * one instance of the SplittableRandom algorithm had been |
| * created for each thread, each with a distinct gamma parameter |
| * (calculated from the thread id). |
| * |
| * Because this class is in a different package than class Thread, |
| * field access methods use Unsafe to bypass access control rules. |
| * To conform to the requirements of the Random superclass |
| * constructor, the common static ThreadLocalRandom maintains an |
| * "initialized" field for the sake of rejecting user calls to |
| * setSeed while still allowing a call from constructor. Note |
| * that serialization is completely unnecessary because there is |
| * only a static singleton. But we generate a serial form |
| * containing "rnd" and "initialized" fields to ensure |
| * compatibility across versions. |
| * |
| * Implementations of non-core methods are mostly the same as in |
| * SplittableRandom, that were in part derived from a previous |
| * version of this class. |
| * |
| * This implementation of ThreadLocalRandom overrides the |
| * definition of the nextGaussian() method in the class Random, |
| * and instead uses the ziggurat-based algorithm that is the |
| * default for the RandomGenerator interface. |
| */ |
| |
| private static int mix32(long z) { |
| z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
| return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32); |
| } |
| |
| /** |
| * Field used only during singleton initialization. |
| * True when constructor completes. |
| */ |
| boolean initialized; |
| |
| /** Constructor used only for static singleton */ |
| private ThreadLocalRandom() { |
| initialized = true; // false during super() call |
| } |
| |
| /** |
| * Initialize Thread fields for the current thread. Called only |
| * when Thread.threadLocalRandomProbe is zero, indicating that a |
| * thread local seed value needs to be generated. Note that even |
| * though the initialization is purely thread-local, we need to |
| * rely on (static) atomic generators to initialize the values. |
| */ |
| static final void localInit() { |
| int p = probeGenerator.addAndGet(PROBE_INCREMENT); |
| int probe = (p == 0) ? 1 : p; // skip 0 |
| long seed = RandomSupport.mixMurmur64(seeder.getAndAdd(SEEDER_INCREMENT)); |
| Thread t = Thread.currentThread(); |
| U.putLong(t, SEED, seed); |
| U.putInt(t, PROBE, probe); |
| } |
| |
| /** |
| * Returns the current thread's {@code ThreadLocalRandom} object. |
| * Methods of this object should be called only by the current thread, |
| * not by other threads. |
| * |
| * @return the current thread's {@code ThreadLocalRandom} |
| */ |
| public static ThreadLocalRandom current() { |
| if (U.getInt(Thread.currentThread(), PROBE) == 0) |
| localInit(); |
| return instance; |
| } |
| |
| /** |
| * Throws {@code UnsupportedOperationException}. Setting seeds in |
| * this generator is not supported. |
| * |
| * @throws UnsupportedOperationException always |
| */ |
| public void setSeed(long seed) { |
| // only allow call from super() constructor |
| if (initialized) |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * Update the thread local seed value by adding to it the sum |
| * of {@code GOLDEN_GAMMA} (an odd value) and twice the thread id. |
| * This sum is always odd (to guarantee that the generator |
| * has maximum period) and is different for different threads. |
| * Because thread id values are allocated consecutively starting |
| * from 0, the high 32 bits of this sum will be the same as the |
| * high 32 bits of {@code GOLDEN_GAMMA} unless an extremely large |
| * number of threads have been created, and so the overall |
| * value added to the thread local seed value will have at least |
| * fourteen 01 and 10 transitions (see the documentation for the |
| * method {@code mixGamma} in class {@code SplittableRandom}), |
| * which should provide adequate statistical quality for |
| * applications likely to use {@code ThreadLocalRandom}. |
| */ |
| final long nextSeed() { |
| Thread t; long r; // read and update per-thread seed |
| U.putLong(t = Thread.currentThread(), SEED, |
| r = U.getLong(t, SEED) + (t.getId() << 1) + GOLDEN_GAMMA); |
| return r; |
| } |
| |
| /** |
| * Generates a pseudorandom number with the indicated number of |
| * low-order bits. Because this class has no subclasses, this |
| * method cannot be invoked or overridden. |
| * |
| * @param bits random bits |
| * @return the next pseudorandom value from this random number |
| * generator's sequence |
| */ |
| protected int next(int bits) { |
| return nextInt() >>> (32 - bits); |
| } |
| |
| // Within-package utilities |
| |
| /* |
| * Descriptions of the usages of the methods below can be found in |
| * the classes that use them. Briefly, a thread's "probe" value is |
| * a non-zero hash code that (probably) does not collide with |
| * other existing threads with respect to any power of two |
| * collision space. When it does collide, it is pseudo-randomly |
| * adjusted (using a Marsaglia XorShift). The nextSecondarySeed |
| * method is used in the same contexts as ThreadLocalRandom, but |
| * only for transient usages such as random adaptive spin/block |
| * sequences for which a cheap RNG suffices and for which it could |
| * in principle disrupt user-visible statistical properties of the |
| * main ThreadLocalRandom if we were to use it. |
| * |
| * Note: Because of package-protection issues, versions of some |
| * these methods also appear in some subpackage classes. |
| */ |
| |
| /** |
| * Returns the probe value for the current thread without forcing |
| * initialization. Note that invoking ThreadLocalRandom.current() |
| * can be used to force initialization on zero return. |
| */ |
| static final int getProbe() { |
| return U.getInt(Thread.currentThread(), PROBE); |
| } |
| |
| /** |
| * Pseudo-randomly advances and records the given probe value for the |
| * given thread. |
| */ |
| static final int advanceProbe(int probe) { |
| probe ^= probe << 13; // xorshift |
| probe ^= probe >>> 17; |
| probe ^= probe << 5; |
| U.putInt(Thread.currentThread(), PROBE, probe); |
| return probe; |
| } |
| |
| /** |
| * Returns the pseudo-randomly initialized or updated secondary seed. |
| */ |
| static final int nextSecondarySeed() { |
| int r; |
| Thread t = Thread.currentThread(); |
| if ((r = U.getInt(t, SECONDARY)) != 0) { |
| r ^= r << 13; // xorshift |
| r ^= r >>> 17; |
| r ^= r << 5; |
| } |
| else if ((r = mix32(seeder.getAndAdd(SEEDER_INCREMENT))) == 0) |
| r = 1; // avoid zero |
| U.putInt(t, SECONDARY, r); |
| return r; |
| } |
| |
| // Support for other package-private ThreadLocal access |
| |
| /** |
| * Erases ThreadLocals by nulling out Thread maps. |
| */ |
| static final void eraseThreadLocals(Thread thread) { |
| U.putReference(thread, THREADLOCALS, null); |
| U.putReference(thread, INHERITABLETHREADLOCALS, null); |
| } |
| |
| static final void setInheritedAccessControlContext(Thread thread, |
| @SuppressWarnings("removal") AccessControlContext acc) { |
| U.putReferenceRelease(thread, INHERITEDACCESSCONTROLCONTEXT, acc); |
| } |
| |
| // Serialization support |
| |
| private static final long serialVersionUID = -5851777807851030925L; |
| |
| /** |
| * @serialField rnd long |
| * seed for random computations |
| * @serialField initialized boolean |
| * always true |
| */ |
| private static final ObjectStreamField[] serialPersistentFields = { |
| new ObjectStreamField("rnd", long.class), |
| new ObjectStreamField("initialized", boolean.class), |
| }; |
| |
| /** |
| * Saves the {@code ThreadLocalRandom} to a stream (that is, serializes it). |
| * @param s the stream |
| * @throws java.io.IOException if an I/O error occurs |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| |
| java.io.ObjectOutputStream.PutField fields = s.putFields(); |
| fields.put("rnd", U.getLong(Thread.currentThread(), SEED)); |
| fields.put("initialized", true); |
| s.writeFields(); |
| } |
| |
| /** |
| * Returns the {@link #current() current} thread's {@code ThreadLocalRandom}. |
| * @return the {@link #current() current} thread's {@code ThreadLocalRandom} |
| */ |
| private Object readResolve() { |
| return current(); |
| } |
| |
| // Static initialization |
| |
| /** |
| * The seed increment. This must be an odd value for the generator to |
| * have the maximum period (2 to the 64th power). |
| * |
| * The value 0x9e3779b97f4a7c15L is odd, and moreover consists of the |
| * first 64 bits of the fractional part of the golden ratio, |
| * which is known to generate good Weyl sequences. |
| */ |
| private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
| |
| /** |
| * The increment for generating probe values. |
| */ |
| private static final int PROBE_INCREMENT = 0x9e3779b9; |
| |
| /** |
| * The increment of seeder per new instance. |
| */ |
| private static final long SEEDER_INCREMENT = 0xbb67ae8584caa73bL; |
| |
| // IllegalArgumentException messages |
| static final String BAD_BOUND = "bound must be positive"; |
| static final String BAD_RANGE = "bound must be greater than origin"; |
| static final String BAD_SIZE = "size must be non-negative"; |
| |
| // Unsafe mechanics |
| private static final Unsafe U = Unsafe.getUnsafe(); |
| private static final long SEED |
| = U.objectFieldOffset(Thread.class, "threadLocalRandomSeed"); |
| private static final long PROBE |
| = U.objectFieldOffset(Thread.class, "threadLocalRandomProbe"); |
| private static final long SECONDARY |
| = U.objectFieldOffset(Thread.class, "threadLocalRandomSecondarySeed"); |
| private static final long THREADLOCALS |
| = U.objectFieldOffset(Thread.class, "threadLocals"); |
| private static final long INHERITABLETHREADLOCALS |
| = U.objectFieldOffset(Thread.class, "inheritableThreadLocals"); |
| private static final long INHERITEDACCESSCONTROLCONTEXT |
| = U.objectFieldOffset(Thread.class, "inheritedAccessControlContext"); |
| |
| /** Generates per-thread initialization/probe field */ |
| private static final AtomicInteger probeGenerator = new AtomicInteger(); |
| |
| /** The common ThreadLocalRandom */ |
| private static final ThreadLocalRandom instance = new ThreadLocalRandom(); |
| |
| /** |
| * The next seed for default constructors. |
| */ |
| private static final AtomicLong seeder |
| = new AtomicLong(RandomSupport.mixMurmur64(System.currentTimeMillis()) ^ |
| RandomSupport.mixMurmur64(System.nanoTime())); |
| |
| // at end of <clinit> to survive static initialization circularity |
| static { |
| String sec = VM.getSavedProperty("java.util.secureRandomSeed"); |
| if (Boolean.parseBoolean(sec)) { |
| byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
| long s = (long)seedBytes[0] & 0xffL; |
| for (int i = 1; i < 8; ++i) |
| s = (s << 8) | ((long)seedBytes[i] & 0xffL); |
| seeder.set(s); |
| } |
| } |
| |
| @SuppressWarnings("serial") |
| private static final class ThreadLocalRandomProxy extends Random { |
| static final Random PROXY = new ThreadLocalRandomProxy(); |
| |
| public int nextInt() { |
| return ThreadLocalRandom.current().nextInt(); |
| } |
| |
| public long nextLong() { |
| return ThreadLocalRandom.current().nextLong(); |
| } |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public boolean nextBoolean() { |
| return super.nextBoolean(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public int nextInt() { |
| return mix32(nextSeed()); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| @Override |
| public int nextInt(int bound) { |
| return super.nextInt(bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| @Override |
| public int nextInt(int origin, int bound) { |
| return super.nextInt(origin, bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public long nextLong() { |
| return RandomSupport.mixMurmur64(nextSeed()); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| @Override |
| public long nextLong(long bound) { |
| return super.nextLong(bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| */ |
| @Override |
| public long nextLong(long origin, long bound) { |
| return super.nextLong(origin, bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public float nextFloat() { |
| return super.nextFloat(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implNote {@inheritDoc} |
| */ |
| @Override |
| public float nextFloat(float bound) { |
| return super.nextFloat(bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implNote {@inheritDoc} |
| */ |
| @Override |
| public float nextFloat(float origin, float bound) { |
| return super.nextFloat(origin, bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public double nextDouble() { |
| return super.nextDouble(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implNote {@inheritDoc} |
| */ |
| @Override |
| public double nextDouble(double bound) { |
| return super.nextDouble(bound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implNote {@inheritDoc} |
| */ |
| @Override |
| public double nextDouble(double origin, double bound) { |
| return super.nextDouble(origin, bound); |
| } |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public IntStream ints(long streamSize) { |
| return AbstractSpliteratorGenerator.ints(ThreadLocalRandomProxy.PROXY, streamSize); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code ints(Long.MAX_VALUE)}. |
| * @since 1.8 |
| */ |
| @Override |
| public IntStream ints() { |
| return AbstractSpliteratorGenerator.ints(ThreadLocalRandomProxy.PROXY); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) { |
| return AbstractSpliteratorGenerator.ints(ThreadLocalRandomProxy.PROXY, streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public IntStream ints(int randomNumberOrigin, int randomNumberBound) { |
| return AbstractSpliteratorGenerator.ints(ThreadLocalRandomProxy.PROXY, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public LongStream longs(long streamSize) { |
| return AbstractSpliteratorGenerator.longs(ThreadLocalRandomProxy.PROXY, streamSize); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code longs(Long.MAX_VALUE)}. |
| * @since 1.8 |
| */ |
| @Override |
| public LongStream longs() { |
| return AbstractSpliteratorGenerator.longs(ThreadLocalRandomProxy.PROXY); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) { |
| return AbstractSpliteratorGenerator.longs(ThreadLocalRandomProxy.PROXY, streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public LongStream longs(long randomNumberOrigin, long randomNumberBound) { |
| return AbstractSpliteratorGenerator.longs(ThreadLocalRandomProxy.PROXY, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public DoubleStream doubles(long streamSize) { |
| return AbstractSpliteratorGenerator.doubles(ThreadLocalRandomProxy.PROXY, streamSize); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code doubles(Long.MAX_VALUE)}. |
| * @since 1.8 |
| */ |
| @Override |
| public DoubleStream doubles() { |
| return AbstractSpliteratorGenerator.doubles(ThreadLocalRandomProxy.PROXY); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) { |
| return AbstractSpliteratorGenerator.doubles(ThreadLocalRandomProxy.PROXY, streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implNote This method is implemented to be equivalent to |
| * {@code doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @since 1.8 |
| */ |
| @Override |
| public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) { |
| return AbstractSpliteratorGenerator.doubles(ThreadLocalRandomProxy.PROXY, randomNumberOrigin, randomNumberBound); |
| } |
| |
| } |
