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.util.concurrent.Executors;
020import java.util.concurrent.ThreadFactory;
021import java.util.concurrent.atomic.AtomicLong;
022
023import org.apache.commons.lang3.Validate;
024
025/**
026 * <p>
027 * An implementation of the {@code ThreadFactory} interface that provides some
028 * configuration options for the threads it creates.
029 * </p>
030 * <p>
031 * A {@code ThreadFactory} is used for instance by an {@code ExecutorService} to
032 * create the threads it uses for executing tasks. In many cases users do not
033 * have to care about a {@code ThreadFactory} because the default one used by an
034 * {@code ExecutorService} will do. However, if there are special requirements
035 * for the threads, a custom {@code 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 {@code UncaughtExceptionHandler} for the thread. This handler is
060 * called if an uncaught exception occurs within the thread.</li>
061 * </ul>
062 * <p>
063 * {@code 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 {@code ThreadFactory} is
067 * used.
068 * </p>
069 * <p>
070 * Instances of {@code BasicThreadFactory} are not created directly, but the
071 * nested {@code 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 {@code BasicThreadFactory} is created and
074 * installed in an {@code 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    /** A counter for the threads created by this factory. */
093    private final AtomicLong threadCounter;
094
095    /** Stores the wrapped factory. */
096    private final ThreadFactory wrappedFactory;
097
098    /** Stores the uncaught exception handler. */
099    private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
100
101    /** Stores the naming pattern for newly created threads. */
102    private final String namingPattern;
103
104    /** Stores the priority. */
105    private final Integer priority;
106
107    /** Stores the daemon status flag. */
108    private final Boolean daemonFlag;
109
110    /**
111     * Creates a new instance of {@code ThreadFactoryImpl} and configures it
112     * from the specified {@code Builder} object.
113     *
114     * @param builder the {@code Builder} object
115     */
116    private BasicThreadFactory(final Builder builder) {
117        if (builder.wrappedFactory == null) {
118            wrappedFactory = Executors.defaultThreadFactory();
119        } else {
120            wrappedFactory = builder.wrappedFactory;
121        }
122
123        namingPattern = builder.namingPattern;
124        priority = builder.priority;
125        daemonFlag = builder.daemonFlag;
126        uncaughtExceptionHandler = builder.exceptionHandler;
127
128        threadCounter = new AtomicLong();
129    }
130
131    /**
132     * Returns the wrapped {@code ThreadFactory}. This factory is used for
133     * actually creating threads. This method never returns <b>null</b>. If no
134     * {@code ThreadFactory} was passed when this object was created, a default
135     * thread factory is returned.
136     *
137     * @return the wrapped {@code ThreadFactory}
138     */
139    public final ThreadFactory getWrappedFactory() {
140        return wrappedFactory;
141    }
142
143    /**
144     * Returns the naming pattern for naming newly created threads. Result can
145     * be <b>null</b> if no naming pattern was provided.
146     *
147     * @return the naming pattern
148     */
149    public final String getNamingPattern() {
150        return namingPattern;
151    }
152
153    /**
154     * Returns the daemon flag. This flag determines whether newly created
155     * threads should be daemon threads. If <b>true</b>, this factory object
156     * calls {@code setDaemon(true)} on the newly created threads. Result can be
157     * <b>null</b> if no daemon flag was provided at creation time.
158     *
159     * @return the daemon flag
160     */
161    public final Boolean getDaemonFlag() {
162        return daemonFlag;
163    }
164
165    /**
166     * Returns the priority of the threads created by this factory. Result can
167     * be <b>null</b> if no priority was specified.
168     *
169     * @return the priority for newly created threads
170     */
171    public final Integer getPriority() {
172        return priority;
173    }
174
175    /**
176     * Returns the {@code UncaughtExceptionHandler} for the threads created by
177     * this factory. Result can be <b>null</b> if no handler was provided.
178     *
179     * @return the {@code UncaughtExceptionHandler}
180     */
181    public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
182        return uncaughtExceptionHandler;
183    }
184
185    /**
186     * Returns the number of threads this factory has already created. This
187     * class maintains an internal counter that is incremented each time the
188     * {@link #newThread(Runnable)} method is invoked.
189     *
190     * @return the number of threads created by this factory
191     */
192    public long getThreadCount() {
193        return threadCounter.get();
194    }
195
196    /**
197     * Creates a new thread. This implementation delegates to the wrapped
198     * factory for creating the thread. Then, on the newly created thread the
199     * corresponding configuration options are set.
200     *
201     * @param r the {@code Runnable} to be executed by the new thread
202     * @return the newly created thread
203     */
204    @Override
205    public Thread newThread(final Runnable r) {
206        final Thread t = getWrappedFactory().newThread(r);
207        initializeThread(t);
208
209        return t;
210    }
211
212    /**
213     * Initializes the specified thread. This method is called by
214     * {@link #newThread(Runnable)} after a new thread has been obtained from
215     * the wrapped thread factory. It initializes the thread according to the
216     * options set for this factory.
217     *
218     * @param t the thread to be initialized
219     */
220    private void initializeThread(final Thread t) {
221
222        if (getNamingPattern() != null) {
223            final Long count = Long.valueOf(threadCounter.incrementAndGet());
224            t.setName(String.format(getNamingPattern(), count));
225        }
226
227        if (getUncaughtExceptionHandler() != null) {
228            t.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
229        }
230
231        if (getPriority() != null) {
232            t.setPriority(getPriority().intValue());
233        }
234
235        if (getDaemonFlag() != null) {
236            t.setDaemon(getDaemonFlag().booleanValue());
237        }
238    }
239
240    /**
241     * <p>
242     * A <em>builder</em> class for creating instances of {@code
243     * BasicThreadFactory}.
244     * </p>
245     * <p>
246     * Using this builder class instances of {@code BasicThreadFactory} can be
247     * created and initialized. The class provides methods that correspond to
248     * the configuration options supported by {@code BasicThreadFactory}. Method
249     * chaining is supported. Refer to the documentation of {@code
250     * BasicThreadFactory} for a usage example.
251     * </p>
252     *
253     */
254    public static class Builder
255        implements org.apache.commons.lang3.builder.Builder<BasicThreadFactory> {
256
257        /** The wrapped factory. */
258        private ThreadFactory wrappedFactory;
259
260        /** The uncaught exception handler. */
261        private Thread.UncaughtExceptionHandler exceptionHandler;
262
263        /** The naming pattern. */
264        private String namingPattern;
265
266        /** The priority. */
267        private Integer priority;
268
269        /** The daemon flag. */
270        private Boolean daemonFlag;
271
272        /**
273         * Sets the {@code ThreadFactory} to be wrapped by the new {@code
274         * BasicThreadFactory}.
275         *
276         * @param factory the wrapped {@code ThreadFactory} (must not be
277         * <b>null</b>)
278         * @return a reference to this {@code Builder}
279         * @throws NullPointerException if the passed in {@code ThreadFactory}
280         * is <b>null</b>
281         */
282        public Builder wrappedFactory(final ThreadFactory factory) {
283            Validate.notNull(factory, "Wrapped ThreadFactory must not be null!");
284
285            wrappedFactory = factory;
286            return this;
287        }
288
289        /**
290         * Sets the naming pattern to be used by the new {@code
291         * BasicThreadFactory}.
292         *
293         * @param pattern the naming pattern (must not be <b>null</b>)
294         * @return a reference to this {@code Builder}
295         * @throws NullPointerException if the naming pattern is <b>null</b>
296         */
297        public Builder namingPattern(final String pattern) {
298            Validate.notNull(pattern, "Naming pattern must not be null!");
299
300            namingPattern = pattern;
301            return this;
302        }
303
304        /**
305         * Sets the daemon flag for the new {@code BasicThreadFactory}. If this
306         * flag is set to <b>true</b> the new thread factory will create daemon
307         * threads.
308         *
309         * @param f the value of the daemon flag
310         * @return a reference to this {@code Builder}
311         */
312        public Builder daemon(final boolean f) {
313            daemonFlag = Boolean.valueOf(f);
314            return this;
315        }
316
317        /**
318         * Sets the priority for the threads created by the new {@code
319         * BasicThreadFactory}.
320         *
321         * @param prio the priority
322         * @return a reference to this {@code Builder}
323         */
324        public Builder priority(final int prio) {
325            priority = Integer.valueOf(prio);
326            return this;
327        }
328
329        /**
330         * Sets the uncaught exception handler for the threads created by the
331         * new {@code BasicThreadFactory}.
332         *
333         * @param handler the {@code UncaughtExceptionHandler} (must not be
334         * <b>null</b>)
335         * @return a reference to this {@code Builder}
336         * @throws NullPointerException if the exception handler is <b>null</b>
337         */
338        public Builder uncaughtExceptionHandler(
339                final Thread.UncaughtExceptionHandler handler) {
340            Validate.notNull(handler, "Uncaught exception handler must not be null!");
341
342            exceptionHandler = handler;
343            return this;
344        }
345
346        /**
347         * Resets this builder. All configuration options are set to default
348         * values. Note: If the {@link #build()} method was called, it is not
349         * necessary to call {@code reset()} explicitly because this is done
350         * automatically.
351         */
352        public void reset() {
353            wrappedFactory = null;
354            exceptionHandler = null;
355            namingPattern = null;
356            priority = null;
357            daemonFlag = null;
358        }
359
360        /**
361         * Creates a new {@code BasicThreadFactory} with all configuration
362         * options that have been specified by calling methods on this builder.
363         * After creating the factory {@link #reset()} is called.
364         *
365         * @return the new {@code BasicThreadFactory}
366         */
367        @Override
368        public BasicThreadFactory build() {
369            final BasicThreadFactory factory = new BasicThreadFactory(this);
370            reset();
371            return factory;
372        }
373    }
374}