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/*
* Java Genetic Algorithm Library (jenetics-4.0.0).
* Copyright (c) 2007-2017 Franz Wilhelmstötter
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Author:
* Franz Wilhelmstötter ([email protected])
*/
package io.jenetics.util;
import static java.util.Objects.requireNonNull;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
import io.jenetics.internal.util.require;
/**
* This class holds the {@link Random} engine used for the GA. The
* {@code RandomRegistry} is thread safe. The registry is initialized with the
* {@link ThreadLocalRandom} PRNG, which has a much better performance behavior
* than an instance of the {@code Random} class. Alternatively, you can
* initialize the registry with one of the PRNG, which are being part of the
* library.
*
*
* Setup of a global PRNG
*
*
{@code
* public class GA {
* public static void main(final String[] args) {
* // Initialize the registry with a ThreadLocal instance of the PRGN.
* // This is the preferred way setting a new PRGN.
* RandomRegistry.setRandom(new LCG64ShiftRandom.ThreadLocal());
*
* // Using a thread safe variant of the PRGN. Leads to slower PRN
* // generation, but gives you the possibility to set a PRNG seed.
* RandomRegistry.setRandom(new LCG64ShiftRandom.ThreadSafe(1234));
*
* ...
* final EvolutionResult result = stream
* .limit(100)
* .collect(toBestEvolutionResult());
* }
* }
* }
*
*
* Setup of a local PRNG
*
* You can temporarily (and locally) change the implementation of the PRNG. E.g.
* for initialize the engine stream with the same initial population.
*
*
{@code
* public class GA {
* public static void main(final String[] args) {
* // Create a reproducible list of genotypes.
* final List> genotypes =
* with(new LCG64ShiftRandom(123), r ->
* Genotype.of(DoubleChromosome.of(0, 10)).instances()
* .limit(50)
* .collect(toList())
* );
*
* final Engine engine = ...;
* final EvolutionResult result = engine
* // Initialize the evolution stream with the given genotypes.
* .stream(genotypes)
* .limit(100)
* .collect(toBestEvolutionResult());
* }
* }
* }
*
*
* @see Random
* @see ThreadLocalRandom
*
* @author Franz Wilhelmstötter
* @since 1.0
* @version 3.0
*/
public final class RandomRegistry {
private RandomRegistry() {require.noInstance();}
private static final Context> CONTEXT =
new Context<>(ThreadLocalRandom::current);
/**
* Return the global {@link Random} object.
*
* @return the global {@link Random} object.
*/
public static Random getRandom() {
return CONTEXT.get().get();
}
static Random random() {
return CONTEXT.get().get();
}
/**
* Set the new global {@link Random} object for the GA. The given
* {@link Random} must be thread safe, which is the case for the
* default Java {@code Random} implementation.
*
* Setting a thread-local random object leads, in general, to a faster
* PRN generation, because the given {@code Random} engine don't have to be
* thread-safe.
*
* @see #setRandom(ThreadLocal)
*
* @param random the new global {@link Random} object for the GA.
* @throws NullPointerException if the {@code random} object is {@code null}.
*/
public static void setRandom(final Random random) {
requireNonNull(random, "Random must not be null.");
CONTEXT.set(() -> random);
}
/**
* Set the new global {@link Random} object for the GA. The given
* {@link Random} don't have be thread safe, because the given
* {@link ThreadLocal} wrapper guarantees thread safety. Setting a
* thread-local random object leads, in general, to a faster
* PRN generation, when using a non-blocking PRNG. This is the preferred
* way for changing the PRNG.
*
* @param random the thread-local random engine to use.
* @throws NullPointerException if the {@code random} object is {@code null}.
*/
@SuppressWarnings("unchecked")
public static void setRandom(final ThreadLocal random) {
requireNonNull(random, "Random must not be null.");
CONTEXT.set(random::get);
}
/**
* Set the random object to it's default value. The default used PRNG
* is the {@link ThreadLocalRandom} PRNG.
*/
public static void reset() {
CONTEXT.reset();
}
/**
* Executes the consumer code using the given {@code random} engine.
*
*
{@code
* final MSeq seq = ...
* using(new Random(123), r -> {
* seq.shuffle();
* });
* }
*
* The example above shuffles the given integer {@code seq} using the
* given {@code Random(123)} engine.
*
* @since 3.0
*
* @param random the PRNG used within the consumer
* @param consumer the consumer which is executed with the scope of
* the given {@code random} engine.
* @param the type of the random engine
* @throws NullPointerException if one of the arguments is {@code null}
*/
public static void using(
final R random,
final Consumer consumer
) {
CONTEXT.with(() -> random, r -> {
consumer.accept(random);
return null;
});
}
/**
* Executes the consumer code using the given {@code random} engine.
*
* {@code
* final MSeq seq = ...
* using(new LCG64ShiftRandom.ThreadLocal(), r -> {
* seq.shuffle();
* });
* }
*
* The example above shuffles the given integer {@code seq} using the
* given {@code LCG64ShiftRandom.ThreadLocal()} engine.
*
* @since 3.0
*
* @param random the PRNG used within the consumer
* @param consumer the consumer which is executed with the scope of
* the given {@code random} engine.
* @param the type of the random engine
* @throws NullPointerException if one of the arguments is {@code null}
*/
public static void using(
final ThreadLocal random,
final Consumer consumer
) {
CONTEXT.with(random::get, r -> {
consumer.accept(random.get());
return null;
});
}
/**
* Opens a new {@code Scope} with the given random engine and executes the
* given function within it. The following example shows how to create a
* reproducible list of genotypes:
* {@code
* final List> genotypes =
* with(new LCG64ShiftRandom(123), r ->
* Genotype.of(DoubleChromosome.of(0, 10)).instances()
* .limit(50)
* .collect(toList())
* );
* }
*
* @since 3.0
*
* @param the type of the random engine
* @param the function return type
* @param random the PRNG used for the opened scope
* @param function the function to apply within the random scope
* @return the object returned by the given function
* @throws NullPointerException if one of the arguments is {@code null}
*/
public static T with(
final R random,
final Function function
) {
return CONTEXT.with(() -> random, s -> function.apply(random));
}
/**
* Opens a new {@code Scope} with the given random engine and executes the
* given function within it. The following example shows how to create a
* reproducible list of genotypes:
* {@code
* final List> genotypes =
* with(new LCG64ShiftRandom.ThreadLocal(), random ->
* Genotype.of(DoubleChromosome.of(0, 10)).instances()
* .limit(50)
* .collect(toList())
* );
* }
*
* @since 3.0
*
* @param the type of the random engine
* @param the function return type
* @param random the PRNG used for the opened scope
* @param function the function to apply within the random scope
* @return the object returned by the given function
* @throws NullPointerException if one of the arguments is {@code null}.
*/
public static T with(
final ThreadLocal random,
final Function function
) {
return CONTEXT.with(random::get, s -> function.apply(random.get()));
}
}