JDK 17 java.base.jmod - Base Module
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⏎ java/util/SplittableRandom.java
/*
* Copyright (c) 2013, 2021, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;
import java.math.BigInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.random.RandomGenerator;
import java.util.random.RandomGenerator.SplittableGenerator;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
import java.util.stream.Stream;
import jdk.internal.util.random.RandomSupport;
import jdk.internal.util.random.RandomSupport.AbstractSplittableGenerator;
import jdk.internal.util.random.RandomSupport.RandomGeneratorProperties;
/**
* A generator of uniform pseudorandom values (with period 2<sup>64</sup>)
* applicable for use in (among other contexts) isolated parallel
* computations that may generate subtasks. Class {@code SplittableRandom}
* supports methods for producing pseudorandom numbers of type {@code int},
* {@code long}, and {@code double} with similar usages as for class
* {@link java.util.Random} but differs in the following ways:
*
* <ul>
*
* <li>Series of generated values pass the DieHarder suite testing
* independence and uniformity properties of random number generators.
* (Most recently validated with <a
* href="http://www.phy.duke.edu/~rgb/General/dieharder.php"> version
* 3.31.1</a>.) These tests validate only the methods for certain
* types and ranges, but similar properties are expected to hold, at
* least approximately, for others as well. The <em>period</em>
* (length of any series of generated values before it repeats) is
* 2<sup>64</sup>. </li>
*
* <li> Method {@link #split} constructs and returns a new
* SplittableRandom instance that shares no mutable state with the
* current instance. However, with very high probability, the
* values collectively generated by the two objects have the same
* statistical properties as if the same quantity of values were
* generated by a single thread using a single {@code
* SplittableRandom} object. </li>
*
* <li>Instances of SplittableRandom are <em>not</em> thread-safe.
* They are designed to be split, not shared, across threads. For
* example, a {@link java.util.concurrent.ForkJoinTask
* fork/join-style} computation using random numbers might include a
* construction of the form {@code new
* Subtask(aSplittableRandom.split()).fork()}.
*
* <li>This class provides additional methods for generating random
* streams, that employ the above techniques when used in {@code
* stream.parallel()} mode.</li>
*
* </ul>
*
* <p>Instances of {@code SplittableRandom} 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}.
*
* @author Guy Steele
* @author Doug Lea
* @since 1.8
*/
@RandomGeneratorProperties(
name = "SplittableRandom",
i = 64, j = 0, k = 0,
equidistribution = 1
)
public final class SplittableRandom implements RandomGenerator, SplittableGenerator {
/*
* Implementation Overview.
*
* This algorithm was inspired by the "DotMix" algorithm by
* Leiserson, Schardl, and Sukha "Deterministic Parallel
* Random-Number Generation for Dynamic-Multithreading Platforms",
* PPoPP 2012, as well as those in "Parallel random numbers: as
* easy as 1, 2, 3" by Salmon, Morae, Dror, and Shaw, SC 2011. It
* differs mainly in simplifying and cheapening operations.
*
* The primary update step (method nextSeed()) is to add a
* constant ("gamma") to the current (64 bit) seed, forming a
* simple sequence. The seed and the gamma values for any two
* SplittableRandom instances are highly likely to be different.
*
* Methods nextLong, nextInt, and derivatives do not return the
* sequence (seed) values, but instead a hash-like bit-mix of
* their bits, producing more independently distributed sequences.
* For nextLong, the mix64 function is based on David Stafford's
* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
* "Mix13" variant of the "64-bit finalizer" function in Austin
* Appleby's MurmurHash3 algorithm (see
* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32
* function is based on Stafford's Mix04 mix function, but returns
* the upper 32 bits cast as int.
*
* The split operation uses the current generator to form the seed
* and gamma for another SplittableRandom. To conservatively
* avoid potential correlations between seed and value generation,
* gamma selection (method mixGamma) uses different
* (Murmurhash3's) mix constants. To avoid potential weaknesses
* in bit-mixing transformations, we restrict gammas to odd values
* with at least 24 0-1 or 1-0 bit transitions. Rather than
* rejecting candidates with too few or too many bits set, method
* mixGamma flips some bits (which has the effect of mapping at
* most 4 to any given gamma value). This reduces the effective
* set of 64bit odd gamma values by about 2%, and serves as an
* automated screening for sequence constant selection that is
* left as an empirical decision in some other hashing and crypto
* algorithms.
*
* The resulting generator thus transforms a sequence in which
* (typically) many bits change on each step, with an inexpensive
* mixer with good (but less than cryptographically secure)
* avalanching.
*
* The default (no-argument) constructor, in essence, invokes
* split() for a common "defaultGen" SplittableRandom. Unlike
* other cases, this split must be performed in a thread-safe
* manner, so we use an AtomicLong to represent the seed rather
* than use an explicit SplittableRandom. To bootstrap the
* defaultGen, we start off using a seed based on current time
* unless the java.util.secureRandomSeed property is set. This
* serves as a slimmed-down (and insecure) variant of SecureRandom
* that also avoids stalls that may occur when using /dev/random.
*
* It is a relatively simple matter to apply the basic design here
* to use 128 bit seeds. However, emulating 128bit arithmetic and
* carrying around twice the state add more overhead than appears
* warranted for current usages.
*
* File organization: First the non-public methods that constitute
* the main algorithm, then the main public methods, followed by
* some custom spliterator classes needed for stream methods.
*/
/**
* The golden ratio scaled to 64bits, used as the initial gamma
* value for (unsplit) SplittableRandoms.
*/
private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L;
/**
* The seed. Updated only via method nextSeed.
*/
private long seed;
/**
* The step value.
*/
private final long gamma;
/**
* Internal constructor used by all others except default constructor.
*/
private SplittableRandom(long seed, long gamma) {
this.seed = seed;
this.gamma = gamma;
this.proxy = new AbstractSplittableGeneratorProxy();
}
/**
* Computes Stafford variant 13 of 64bit mix function.
* http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html
*/
private static long mix64(long z) {
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
return z ^ (z >>> 31);
}
/**
* Returns the 32 high bits of Stafford variant 4 mix64 function as int.
* http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html
*/
private static int mix32(long z) {
z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L;
return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32);
}
/**
* Returns the gamma value to use for a new split instance.
* Uses the 64bit mix function from MurmurHash3.
* https://github.com/aappleby/smhasher/wiki/MurmurHash3
*/
private static long mixGamma(long z) {
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
z = (z ^ (z >>> 33)) | 1L; // force to be odd
int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions
return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z;
}
/**
* Proxy class to non-public RandomSupportAbstractSplittableGenerator.
*/
private class AbstractSplittableGeneratorProxy extends AbstractSplittableGenerator {
@Override
public int nextInt() {
return SplittableRandom.this.nextInt();
}
@Override
public long nextLong() {
return SplittableRandom.this.nextLong();
}
@Override
public java.util.SplittableRandom split(SplittableGenerator source) {
return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong()));
}
}
/**
* Proxy object to non-public RandomSupportAbstractSplittableGenerator.
*/
private AbstractSplittableGeneratorProxy proxy;
/**
* Adds gamma to seed.
*/
private long nextSeed() {
return seed += gamma;
}
/**
* The seed generator for default constructors.
*/
private static final AtomicLong defaultGen = new AtomicLong(RandomSupport.initialSeed());
/* ---------------- public methods ---------------- */
/**
* Creates a new SplittableRandom instance using the specified
* initial seed. SplittableRandom instances created with the same
* seed in the same program generate identical sequences of values.
*
* @param seed the initial seed
*/
public SplittableRandom(long seed) {
this(seed, GOLDEN_GAMMA);
}
/**
* Creates a new SplittableRandom instance that is likely to
* generate sequences of values that are statistically independent
* of those of any other instances in the current program; and
* may, and typically does, vary across program invocations.
*/
public SplittableRandom() { // emulate defaultGen.split()
long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA);
this.seed = mix64(s);
this.gamma = mixGamma(s + GOLDEN_GAMMA);
this.proxy = new AbstractSplittableGeneratorProxy();
}
/**
* Constructs and returns a new SplittableRandom instance that
* shares no mutable state with this instance. However, with very
* high probability, the set of values collectively generated by
* the two objects has the same statistical properties as if the
* same quantity of values were generated by a single thread using
* a single SplittableRandom object. Either or both of the two
* objects may be further split using the {@code split()} method,
* and the same expected statistical properties apply to the
* entire set of generators constructed by such recursive
* splitting.
*
* @return the new SplittableRandom instance
*/
public SplittableRandom split() {
return new SplittableRandom(nextLong(), mixGamma(nextSeed()));
}
/**
* {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @since 17
*/
public SplittableRandom split(SplittableGenerator source) {
return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong()));
}
@Override
public int nextInt() {
return mix32(nextSeed());
}
@Override
public long nextLong() {
return mix64(nextSeed());
}
/**
* {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @since 10
*/
@Override
public void nextBytes(byte[] bytes) {
proxy.nextBytes(bytes);
}
/**
* {@inheritDoc}
* @implSpec {@inheritDoc}
* @since 17
*/
@Override
public Stream<SplittableGenerator> splits() {
return proxy.splits();
}
/**
* {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @implSpec {@inheritDoc}
* @since 17
*/
@Override
public Stream<SplittableGenerator> splits(long streamSize) {
return proxy.splits(streamSize, this);
}
/**
* {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @implSpec {@inheritDoc}
* @since 17
*/
@Override
public Stream<SplittableGenerator> splits(SplittableGenerator source) {
return proxy.splits(Long.MAX_VALUE, source);
}
/**
* {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
* @implSpec {@inheritDoc}
* @since 17
*/
@Override
public Stream<SplittableGenerator> splits(long streamSize, SplittableGenerator source) {
return proxy.splits(streamSize, source);
}
/**
* Returns a stream producing the given {@code streamSize} number
* of pseudorandom {@code int} values from this generator and/or
* one split from it.
*
* @param streamSize the number of values to generate
* @return a stream of pseudorandom {@code int} values
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
@Override
public IntStream ints(long streamSize) {
return proxy.ints(streamSize);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code int}
* values from this generator and/or one split from it.
*
* @implNote This method is implemented to be equivalent to {@code
* ints(Long.MAX_VALUE)}.
*
* @return a stream of pseudorandom {@code int} values
*/
@Override
public IntStream ints() {
return proxy.ints();
}
/**
* Returns a stream producing the given {@code streamSize} number
* of pseudorandom {@code int} values from this generator and/or one split
* from it; each value conforms to the given origin (inclusive) and bound
* (exclusive).
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) {
return proxy.ints(streamSize, randomNumberOrigin, randomNumberBound);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* int} values from this generator and/or one split from it; each value
* conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
return proxy.ints(randomNumberOrigin, randomNumberBound);
}
/**
* Returns a stream producing the given {@code streamSize} number
* of pseudorandom {@code long} values from this generator and/or
* one split from it.
*
* @param streamSize the number of values to generate
* @return a stream of pseudorandom {@code long} values
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
@Override
public LongStream longs(long streamSize) {
return proxy.longs(streamSize);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* long} values from this generator and/or one split from it.
*
* @implNote This method is implemented to be equivalent to {@code
* longs(Long.MAX_VALUE)}.
*
* @return a stream of pseudorandom {@code long} values
*/
@Override
public LongStream longs() {
return proxy.longs();
}
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code long} values from this generator and/or one split
* from it; each value conforms to the given origin (inclusive) and bound
* (exclusive).
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) {
return proxy.longs(streamSize, randomNumberOrigin, randomNumberBound);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* long} values from this generator and/or one split from it; each value
* conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
return proxy.longs(randomNumberOrigin, randomNumberBound);
}
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code double} values from this generator and/or one split
* from it; each value is between zero (inclusive) and one (exclusive).
*
* @param streamSize the number of values to generate
* @return a stream of {@code double} values
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
*/
@Override
public DoubleStream doubles(long streamSize) {
return proxy.doubles(streamSize);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* double} values from this generator and/or one split from it; each value
* is between zero (inclusive) and one (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* doubles(Long.MAX_VALUE)}.
*
* @return a stream of pseudorandom {@code double} values
*/
@Override
public DoubleStream doubles() {
return proxy.doubles();
}
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code double} values from this generator and/or one split
* from it; each value conforms to the given origin (inclusive) and bound
* (exclusive).
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) {
return proxy.doubles(streamSize, randomNumberOrigin, randomNumberBound);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* double} values from this generator and/or one split from it; each value
* conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@Override
public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
return proxy.doubles(randomNumberOrigin, randomNumberBound);
}
}
⏎ java/util/SplittableRandom.java
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