001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  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 */
017package org.apache.commons.lang3.concurrent;
018
019import java.lang.Thread.UncaughtExceptionHandler;
020import java.util.Objects;
021import java.util.concurrent.ExecutorService;
022import java.util.concurrent.Executors;
023import java.util.concurrent.ThreadFactory;
024import java.util.concurrent.atomic.AtomicLong;
025
026/**
027 * An implementation of the {@link ThreadFactory} interface that provides some
028 * configuration options for the threads it creates.
029 *
030 * <p>
031 * A {@link ThreadFactory} is used for instance by an {@link ExecutorService} to
032 * create the threads it uses for executing tasks. In many cases users do not
033 * have to care about a {@link ThreadFactory} because the default one used by an
034 * {@link ExecutorService} will do. However, if there are special requirements
035 * for the threads, a custom {@link ThreadFactory} has to be created.
036 * </p>
037 * <p>
038 * This class provides some frequently needed configuration options for the
039 * threads it creates. These are the following:
040 * </p>
041 * <ul>
042 * <li>A name pattern for the threads created by this factory can be specified.
043 * This is often useful if an application uses multiple executor services for
044 * different purposes. If the names of the threads used by these services have
045 * meaningful names, log output or exception traces can be much easier to read.
046 * Naming patterns are <em>format strings</em> as used by the {@code
047 * String.format()} method. The string can contain the place holder {@code %d}
048 * which will be replaced by the number of the current thread ({@code
049 * ThreadFactoryImpl} keeps a counter of the threads it has already created).
050 * For instance, the naming pattern {@code "My %d. worker thread"} will result
051 * in thread names like {@code "My 1. worker thread"}, {@code
052 * "My 2. worker thread"} and so on.</li>
053 * <li>A flag whether the threads created by this factory should be daemon
054 * threads. This can impact the exit behavior of the current Java application
055 * because the JVM shuts down if there are only daemon threads running.</li>
056 * <li>The priority of the thread. Here an integer value can be provided. The
057 * {@code java.lang.Thread} class defines constants for valid ranges of priority
058 * values.</li>
059 * <li>The {@link UncaughtExceptionHandler} for the thread. This handler is
060 * called if an uncaught exception occurs within the thread.</li>
061 * </ul>
062 * <p>
063 * {@link BasicThreadFactory} wraps another thread factory which actually
064 * creates new threads. The configuration options are set on the threads created
065 * by the wrapped thread factory. On construction time the factory to be wrapped
066 * can be specified. If none is provided, a default {@link ThreadFactory} is
067 * used.
068 * </p>
069 * <p>
070 * Instances of {@link BasicThreadFactory} are not created directly, but the
071 * nested {@link Builder} class is used for this purpose. Using the builder only
072 * the configuration options an application is interested in need to be set. The
073 * following example shows how a {@link BasicThreadFactory} is created and
074 * installed in an {@link ExecutorService}:
075 * </p>
076 *
077 * <pre>
078 * // Create a factory that produces daemon threads with a naming pattern and
079 * // a priority
080 * BasicThreadFactory factory = new BasicThreadFactory.Builder()
081 *     .namingPattern(&quot;workerthread-%d&quot;)
082 *     .daemon(true)
083 *     .priority(Thread.MAX_PRIORITY)
084 *     .build();
085 * // Create an executor service for single-threaded execution
086 * ExecutorService exec = Executors.newSingleThreadExecutor(factory);
087 * </pre>
088 *
089 * @since 3.0
090 */
091public class BasicThreadFactory implements ThreadFactory {
092    /**
093     * A <em>builder</em> class for creating instances of {@code
094     * BasicThreadFactory}.
095     *
096     * <p>
097     * Using this builder class instances of {@link BasicThreadFactory} can be
098     * created and initialized. The class provides methods that correspond to
099     * the configuration options supported by {@link BasicThreadFactory}. Method
100     * chaining is supported. Refer to the documentation of {@code
101     * BasicThreadFactory} for a usage example.
102     * </p>
103     *
104     */
105    public static class Builder
106        implements org.apache.commons.lang3.builder.Builder<BasicThreadFactory> {
107
108        /** The wrapped factory. */
109        private ThreadFactory wrappedFactory;
110
111        /** The uncaught exception handler. */
112        private Thread.UncaughtExceptionHandler exceptionHandler;
113
114        /** The naming pattern. */
115        private String namingPattern;
116
117        /** The priority. */
118        private Integer priority;
119
120        /** The daemon flag. */
121        private Boolean daemon;
122
123        /**
124         * Creates a new {@link BasicThreadFactory} with all configuration
125         * options that have been specified by calling methods on this builder.
126         * After creating the factory {@link #reset()} is called.
127         *
128         * @return the new {@link BasicThreadFactory}
129         */
130        @Override
131        public BasicThreadFactory build() {
132            final BasicThreadFactory factory = new BasicThreadFactory(this);
133            reset();
134            return factory;
135        }
136
137        /**
138         * Sets the daemon flag for the new {@link BasicThreadFactory}. If this
139         * flag is set to <b>true</b> the new thread factory will create daemon
140         * threads.
141         *
142         * @param daemon the value of the daemon flag
143         * @return a reference to this {@link Builder}
144         */
145        public Builder daemon(final boolean daemon) {
146            this.daemon = Boolean.valueOf(daemon);
147            return this;
148        }
149
150        /**
151         * Sets the naming pattern to be used by the new {@code
152         * BasicThreadFactory}.
153         *
154         * @param pattern the naming pattern (must not be <b>null</b>)
155         * @return a reference to this {@link Builder}
156         * @throws NullPointerException if the naming pattern is <b>null</b>
157         */
158        public Builder namingPattern(final String pattern) {
159            Objects.requireNonNull(pattern, "pattern");
160
161            namingPattern = pattern;
162            return this;
163        }
164
165        /**
166         * Sets the priority for the threads created by the new {@code
167         * BasicThreadFactory}.
168         *
169         * @param priority the priority
170         * @return a reference to this {@link Builder}
171         */
172        public Builder priority(final int priority) {
173            this.priority = Integer.valueOf(priority);
174            return this;
175        }
176
177        /**
178         * Resets this builder. All configuration options are set to default
179         * values. Note: If the {@link #build()} method was called, it is not
180         * necessary to call {@code reset()} explicitly because this is done
181         * automatically.
182         */
183        public void reset() {
184            wrappedFactory = null;
185            exceptionHandler = null;
186            namingPattern = null;
187            priority = null;
188            daemon = null;
189        }
190
191        /**
192         * Sets the uncaught exception handler for the threads created by the
193         * new {@link BasicThreadFactory}.
194         *
195         * @param handler the {@link UncaughtExceptionHandler} (must not be
196         * <b>null</b>)
197         * @return a reference to this {@link Builder}
198         * @throws NullPointerException if the exception handler is <b>null</b>
199         */
200        public Builder uncaughtExceptionHandler(
201                final Thread.UncaughtExceptionHandler handler) {
202            Objects.requireNonNull(handler, "handler");
203
204            exceptionHandler = handler;
205            return this;
206        }
207
208        /**
209         * Sets the {@link ThreadFactory} to be wrapped by the new {@code
210         * BasicThreadFactory}.
211         *
212         * @param factory the wrapped {@link ThreadFactory} (must not be
213         * <b>null</b>)
214         * @return a reference to this {@link Builder}
215         * @throws NullPointerException if the passed in {@link ThreadFactory}
216         * is <b>null</b>
217         */
218        public Builder wrappedFactory(final ThreadFactory factory) {
219            Objects.requireNonNull(factory, "factory");
220
221            wrappedFactory = factory;
222            return this;
223        }
224    }
225
226    /** A counter for the threads created by this factory. */
227    private final AtomicLong threadCounter;
228
229    /** Stores the wrapped factory. */
230    private final ThreadFactory wrappedFactory;
231
232    /** Stores the uncaught exception handler. */
233    private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
234
235    /** Stores the naming pattern for newly created threads. */
236    private final String namingPattern;
237
238    /** Stores the priority. */
239    private final Integer priority;
240
241    /** Stores the daemon status flag. */
242    private final Boolean daemon;
243
244    /**
245     * Creates a new instance of {@link ThreadFactory} and configures it
246     * from the specified {@link Builder} object.
247     *
248     * @param builder the {@link Builder} object
249     */
250    private BasicThreadFactory(final Builder builder) {
251        if (builder.wrappedFactory == null) {
252            wrappedFactory = Executors.defaultThreadFactory();
253        } else {
254            wrappedFactory = builder.wrappedFactory;
255        }
256
257        namingPattern = builder.namingPattern;
258        priority = builder.priority;
259        daemon = builder.daemon;
260        uncaughtExceptionHandler = builder.exceptionHandler;
261
262        threadCounter = new AtomicLong();
263    }
264
265    /**
266     * Returns the daemon flag. This flag determines whether newly created
267     * threads should be daemon threads. If <b>true</b>, this factory object
268     * calls {@code setDaemon(true)} on the newly created threads. Result can be
269     * <b>null</b> if no daemon flag was provided at creation time.
270     *
271     * @return the daemon flag
272     */
273    public final Boolean getDaemonFlag() {
274        return daemon;
275    }
276
277    /**
278     * Returns the naming pattern for naming newly created threads. Result can
279     * be <b>null</b> if no naming pattern was provided.
280     *
281     * @return the naming pattern
282     */
283    public final String getNamingPattern() {
284        return namingPattern;
285    }
286
287    /**
288     * Returns the priority of the threads created by this factory. Result can
289     * be <b>null</b> if no priority was specified.
290     *
291     * @return the priority for newly created threads
292     */
293    public final Integer getPriority() {
294        return priority;
295    }
296
297    /**
298     * Returns the number of threads this factory has already created. This
299     * class maintains an internal counter that is incremented each time the
300     * {@link #newThread(Runnable)} method is invoked.
301     *
302     * @return the number of threads created by this factory
303     */
304    public long getThreadCount() {
305        return threadCounter.get();
306    }
307
308    /**
309     * Returns the {@link UncaughtExceptionHandler} for the threads created by
310     * this factory. Result can be <b>null</b> if no handler was provided.
311     *
312     * @return the {@link UncaughtExceptionHandler}
313     */
314    public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
315        return uncaughtExceptionHandler;
316    }
317
318    /**
319     * Returns the wrapped {@link ThreadFactory}. This factory is used for
320     * actually creating threads. This method never returns <b>null</b>. If no
321     * {@link ThreadFactory} was passed when this object was created, a default
322     * thread factory is returned.
323     *
324     * @return the wrapped {@link ThreadFactory}
325     */
326    public final ThreadFactory getWrappedFactory() {
327        return wrappedFactory;
328    }
329
330    /**
331     * Initializes the specified thread. This method is called by
332     * {@link #newThread(Runnable)} after a new thread has been obtained from
333     * the wrapped thread factory. It initializes the thread according to the
334     * options set for this factory.
335     *
336     * @param thread the thread to be initialized
337     */
338    private void initializeThread(final Thread thread) {
339
340        if (getNamingPattern() != null) {
341            final Long count = Long.valueOf(threadCounter.incrementAndGet());
342            thread.setName(String.format(getNamingPattern(), count));
343        }
344
345        if (getUncaughtExceptionHandler() != null) {
346            thread.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
347        }
348
349        if (getPriority() != null) {
350            thread.setPriority(getPriority().intValue());
351        }
352
353        if (getDaemonFlag() != null) {
354            thread.setDaemon(getDaemonFlag().booleanValue());
355        }
356    }
357
358    /**
359     * Creates a new thread. This implementation delegates to the wrapped
360     * factory for creating the thread. Then, on the newly created thread the
361     * corresponding configuration options are set.
362     *
363     * @param runnable the {@link Runnable} to be executed by the new thread
364     * @return the newly created thread
365     */
366    @Override
367    public Thread newThread(final Runnable runnable) {
368        final Thread thread = getWrappedFactory().newThread(runnable);
369        initializeThread(thread);
370
371        return thread;
372    }
373}