001 /*
002 * Java Genetic Algorithm Library (jenetics-5.0.0).
003 * Copyright (c) 2007-2019 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.setRandom(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.setRandom(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 getRandom() {
107 return CONTEXT.get().get();
108 }
109
110 static Random random() {
111 return CONTEXT.get().get();
112 }
113
114 /**
115 * Set the new global {@link Random} object for the GA. The given
116 * {@link Random} <b>must</b> be thread safe, which is the case for the
117 * default Java {@code Random} implementation.
118 * <p>
119 * Setting a <i>thread-local</i> random object leads, in general, to a faster
120 * PRN generation, because the given {@code Random} engine don't have to be
121 * thread-safe.
122 *
123 * @see #setRandom(ThreadLocal)
124 *
125 * @param random the new global {@link Random} object for the GA.
126 * @throws NullPointerException if the {@code random} object is {@code null}.
127 */
128 public static void setRandom(final Random random) {
129 requireNonNull(random, "Random must not be null.");
130 CONTEXT.set(() -> random);
131 }
132
133 /**
134 * Set the new global {@link Random} object for the GA. The given
135 * {@link Random} don't have be thread safe, because the given
136 * {@link ThreadLocal} wrapper guarantees thread safety. Setting a
137 * <i>thread-local</i> random object leads, in general, to a faster
138 * PRN generation, when using a non-blocking PRNG. This is the preferred
139 * way for changing the PRNG.
140 *
141 * @param random the thread-local random engine to use.
142 * @throws NullPointerException if the {@code random} object is {@code null}.
143 */
144 @SuppressWarnings("unchecked")
145 public static void setRandom(final ThreadLocal<? extends Random> random) {
146 requireNonNull(random, "Random must not be null.");
147 CONTEXT.set(random::get);
148 }
149
150 /**
151 * Set the random object to it's default value. The <i>default</i> used PRNG
152 * is the {@link ThreadLocalRandom} PRNG.
153 */
154 public static void reset() {
155 CONTEXT.reset();
156 }
157
158 /**
159 * Executes the consumer code using the given {@code random} engine.
160 *
161 * <pre>{@code
162 * final MSeq<Integer> seq = ...
163 * using(new Random(123), r -> {
164 * seq.shuffle();
165 * });
166 * }</pre>
167 *
168 * The example above shuffles the given integer {@code seq} <i>using</i> the
169 * given {@code Random(123)} engine.
170 *
171 * @since 3.0
172 *
173 * @param random the PRNG used within the consumer
174 * @param consumer the consumer which is executed with the <i>scope</i> of
175 * the given {@code random} engine.
176 * @param <R> the type of the random engine
177 * @throws NullPointerException if one of the arguments is {@code null}
178 */
179 public static <R extends Random> void using(
180 final R random,
181 final Consumer<? super R> consumer
182 ) {
183 CONTEXT.with(() -> random, r -> {
184 consumer.accept(random);
185 return null;
186 });
187 }
188
189 /**
190 * Executes the consumer code using the given {@code random} engine.
191 *
192 * <pre>{@code
193 * final MSeq<Integer> seq = ...
194 * using(new LCG64ShiftRandom.ThreadLocal(), r -> {
195 * seq.shuffle();
196 * });
197 * }</pre>
198 *
199 * The example above shuffles the given integer {@code seq} <i>using</i> the
200 * given {@code LCG64ShiftRandom.ThreadLocal()} engine.
201 *
202 * @since 3.0
203 *
204 * @param random the PRNG used within the consumer
205 * @param consumer the consumer which is executed with the <i>scope</i> of
206 * the given {@code random} engine.
207 * @param <R> the type of the random engine
208 * @throws NullPointerException if one of the arguments is {@code null}
209 */
210 public static <R extends Random> void using(
211 final ThreadLocal<R> random,
212 final Consumer<? super R> consumer
213 ) {
214 CONTEXT.with(random::get, r -> {
215 consumer.accept(random.get());
216 return null;
217 });
218 }
219
220 /**
221 * Opens a new {@code Scope} with the given random engine and executes the
222 * given function within it. The following example shows how to create a
223 * reproducible list of genotypes:
224 * <pre>{@code
225 * final List<Genotype<DoubleGene>> genotypes =
226 * with(new LCG64ShiftRandom(123), r ->
227 * Genotype.of(DoubleChromosome.of(0, 10)).instances()
228 * .limit(50)
229 * .collect(toList())
230 * );
231 * }</pre>
232 *
233 * @since 3.0
234 *
235 * @param <R> the type of the random engine
236 * @param <T> the function return type
237 * @param random the PRNG used for the opened scope
238 * @param function the function to apply within the random scope
239 * @return the object returned by the given function
240 * @throws NullPointerException if one of the arguments is {@code null}
241 */
242 public static <R extends Random, T> T with(
243 final R random,
244 final Function<? super R, ? extends T> function
245 ) {
246 return CONTEXT.with(() -> random, s -> function.apply(random));
247 }
248
249 /**
250 * Opens a new {@code Scope} with the given random engine and executes the
251 * given function within it. The following example shows how to create a
252 * reproducible list of genotypes:
253 * <pre>{@code
254 * final List<Genotype<DoubleGene>> genotypes =
255 * with(new LCG64ShiftRandom.ThreadLocal(), random ->
256 * Genotype.of(DoubleChromosome.of(0, 10)).instances()
257 * .limit(50)
258 * .collect(toList())
259 * );
260 * }</pre>
261 *
262 * @since 3.0
263 *
264 * @param <R> the type of the random engine
265 * @param <T> the function return type
266 * @param random the PRNG used for the opened scope
267 * @param function the function to apply within the random scope
268 * @return the object returned by the given function
269 * @throws NullPointerException if one of the arguments is {@code null}.
270 */
271 public static <R extends Random, T> T with(
272 final ThreadLocal<R> random,
273 final Function<? super R, ? extends T> function
274 ) {
275 return CONTEXT.with(random::get, s -> function.apply(random.get()));
276 }
277
278 }
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