001 /*
002 * Java Genetic Algorithm Library (jenetics-6.0.0).
003 * Copyright (c) 2007-2020 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020 package io.jenetics.util;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.Random;
025 import java.util.concurrent.ThreadLocalRandom;
026 import java.util.function.Consumer;
027 import java.util.function.Function;
028 import java.util.function.Supplier;
029
030 /**
031 * This class holds the {@link Random} engine used for the GA. The
032 * {@code RandomRegistry} is thread safe. The registry is initialized with the
033 * {@link ThreadLocalRandom} PRNG, which has a much better performance behavior
034 * than an instance of the {@code Random} class. Alternatively, you can
035 * initialize the registry with one of the PRNG, which are being part of the
036 * library.
037 * <p>
038 *
039 * <b>Setup of a <i>global</i> PRNG</b>
040 *
041 * <pre>{@code
042 * public class GA {
043 * public static void main(final String[] args) {
044 * // Initialize the registry with a ThreadLocal instance of the PRGN.
045 * // This is the preferred way setting a new PRGN.
046 * RandomRegistry.random(new LCG64ShiftRandom.ThreadLocal());
047 *
048 * // Using a thread safe variant of the PRGN. Leads to slower PRN
049 * // generation, but gives you the possibility to set a PRNG seed.
050 * RandomRegistry.random(new LCG64ShiftRandom.ThreadSafe(1234));
051 *
052 * ...
053 * final EvolutionResult<DoubleGene, Double> result = stream
054 * .limit(100)
055 * .collect(toBestEvolutionResult());
056 * }
057 * }
058 * }</pre>
059 * <p>
060 *
061 * <b>Setup of a <i>local</i> PRNG</b><br>
062 *
063 * You can temporarily (and locally) change the implementation of the PRNG. E.g.
064 * for initialize the engine stream with the same initial population.
065 *
066 * <pre>{@code
067 * public class GA {
068 * public static void main(final String[] args) {
069 * // Create a reproducible list of genotypes.
070 * final List<Genotype<DoubleGene>> genotypes =
071 * with(new LCG64ShiftRandom(123), r ->
072 * Genotype.of(DoubleChromosome.of(0, 10)).instances()
073 * .limit(50)
074 * .collect(toList())
075 * );
076 *
077 * final Engine<DoubleGene, Double> engine = ...;
078 * final EvolutionResult<DoubleGene, Double> result = engine
079 * // Initialize the evolution stream with the given genotypes.
080 * .stream(genotypes)
081 * .limit(100)
082 * .collect(toBestEvolutionResult());
083 * }
084 * }
085 * }</pre>
086 * <p>
087 *
088 * @see Random
089 * @see ThreadLocalRandom
090 *
091 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
092 * @since 1.0
093 * @version 3.0
094 */
095 public final class RandomRegistry {
096 private RandomRegistry() {}
097
098 private static final Context<Supplier<Random>> CONTEXT =
099 new Context<>(ThreadLocalRandom::current);
100
101 /**
102 * Return the global {@link Random} object.
103 *
104 * @return the global {@link Random} object.
105 */
106 public static Random random() {
107 return CONTEXT.get().get();
108 }
109
110 /**
111 * Set the new global {@link Random} object for the GA. The given
112 * {@link Random} <b>must</b> be thread safe, which is the case for the
113 * default Java {@code Random} implementation.
114 * <p>
115 * Setting a <i>thread-local</i> random object leads, in general, to a faster
116 * PRN generation, because the given {@code Random} engine don't have to be
117 * thread-safe.
118 *
119 * @see #random(ThreadLocal)
120 *
121 * @param random the new global {@link Random} object for the GA.
122 * @throws NullPointerException if the {@code random} object is {@code null}.
123 */
124 public static void random(final Random random) {
125 requireNonNull(random, "Random must not be null.");
126 CONTEXT.set(() -> random);
127 }
128
129 /**
130 * Set the new global {@link Random} object for the GA. The given
131 * {@link Random} don't have be thread safe, because the given
132 * {@link ThreadLocal} wrapper guarantees thread safety. Setting a
133 * <i>thread-local</i> random object leads, in general, to a faster
134 * PRN generation, when using a non-blocking PRNG. This is the preferred
135 * way for changing the PRNG.
136 *
137 * @param random the thread-local random engine to use.
138 * @throws NullPointerException if the {@code random} object is {@code null}.
139 */
140 public static void random(final ThreadLocal<? extends Random> random) {
141 requireNonNull(random, "Random must not be null.");
142 CONTEXT.set(random::get);
143 }
144
145 /**
146 * Set the random object to it's default value. The <i>default</i> used PRNG
147 * is the {@link ThreadLocalRandom} PRNG.
148 */
149 public static void reset() {
150 CONTEXT.reset();
151 }
152
153 /**
154 * Executes the consumer code using the given {@code random} engine.
155 *
156 * <pre>{@code
157 * final MSeq<Integer> seq = ...
158 * using(new Random(123), r -> {
159 * seq.shuffle();
160 * });
161 * }</pre>
162 *
163 * The example above shuffles the given integer {@code seq} <i>using</i> the
164 * given {@code Random(123)} engine.
165 *
166 * @since 3.0
167 *
168 * @param random the PRNG used within the consumer
169 * @param consumer the consumer which is executed with the <i>scope</i> of
170 * the given {@code random} engine.
171 * @param <R> the type of the random engine
172 * @throws NullPointerException if one of the arguments is {@code null}
173 */
174 public static <R extends Random> void using(
175 final R random,
176 final Consumer<? super R> consumer
177 ) {
178 CONTEXT.with(() -> random, r -> {
179 consumer.accept(random);
180 return null;
181 });
182 }
183
184 /**
185 * Executes the consumer code using the given {@code random} engine.
186 *
187 * <pre>{@code
188 * final MSeq<Integer> seq = ...
189 * using(new LCG64ShiftRandom.ThreadLocal(), r -> {
190 * seq.shuffle();
191 * });
192 * }</pre>
193 *
194 * The example above shuffles the given integer {@code seq} <i>using</i> the
195 * given {@code LCG64ShiftRandom.ThreadLocal()} engine.
196 *
197 * @since 3.0
198 *
199 * @param random the PRNG used within the consumer
200 * @param consumer the consumer which is executed with the <i>scope</i> of
201 * the given {@code random} engine.
202 * @param <R> the type of the random engine
203 * @throws NullPointerException if one of the arguments is {@code null}
204 */
205 public static <R extends Random> void using(
206 final ThreadLocal<R> random,
207 final Consumer<? super R> consumer
208 ) {
209 CONTEXT.with(random::get, r -> {
210 consumer.accept(random.get());
211 return null;
212 });
213 }
214
215 /**
216 * Opens a new {@code Scope} with the given random engine and executes the
217 * given function within it. The following example shows how to create a
218 * reproducible list of genotypes:
219 * <pre>{@code
220 * final List<Genotype<DoubleGene>> genotypes =
221 * with(new LCG64ShiftRandom(123), r ->
222 * Genotype.of(DoubleChromosome.of(0, 10)).instances()
223 * .limit(50)
224 * .collect(toList())
225 * );
226 * }</pre>
227 *
228 * @since 3.0
229 *
230 * @param <R> the type of the random engine
231 * @param <T> the function return type
232 * @param random the PRNG used for the opened scope
233 * @param function the function to apply within the random scope
234 * @return the object returned by the given function
235 * @throws NullPointerException if one of the arguments is {@code null}
236 */
237 public static <R extends Random, T> T with(
238 final R random,
239 final Function<? super R, ? extends T> function
240 ) {
241 return CONTEXT.with(() -> random, s -> function.apply(random));
242 }
243
244 /**
245 * Opens a new {@code Scope} with the given random engine and executes the
246 * given function within it. The following example shows how to create a
247 * reproducible list of genotypes:
248 * <pre>{@code
249 * final List<Genotype<DoubleGene>> genotypes =
250 * with(new LCG64ShiftRandom.ThreadLocal(), random ->
251 * Genotype.of(DoubleChromosome.of(0, 10)).instances()
252 * .limit(50)
253 * .collect(toList())
254 * );
255 * }</pre>
256 *
257 * @since 3.0
258 *
259 * @param <R> the type of the random engine
260 * @param <T> the function return type
261 * @param random the PRNG used for the opened scope
262 * @param function the function to apply within the random scope
263 * @return the object returned by the given function
264 * @throws NullPointerException if one of the arguments is {@code null}.
265 */
266 public static <R extends Random, T> T with(
267 final ThreadLocal<R> random,
268 final Function<? super R, ? extends T> function
269 ) {
270 return CONTEXT.with(random::get, s -> function.apply(random.get()));
271 }
272
273 }
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