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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.lang3.concurrent;
18  
19  import java.util.concurrent.Executors;
20  import java.util.concurrent.ThreadFactory;
21  import java.util.concurrent.atomic.AtomicLong;
22  
23  import org.apache.commons.lang3.Validate;
24  
25  /**
26   * <p>
27   * An implementation of the {@code ThreadFactory} interface that provides some
28   * configuration options for the threads it creates.
29   * </p>
30   * <p>
31   * A {@code ThreadFactory} is used for instance by an {@code ExecutorService} to
32   * create the threads it uses for executing tasks. In many cases users do not
33   * have to care about a {@code ThreadFactory} because the default one used by an
34   * {@code ExecutorService} will do. However, if there are special requirements
35   * for the threads, a custom {@code ThreadFactory} has to be created.
36   * </p>
37   * <p>
38   * This class provides some frequently needed configuration options for the
39   * threads it creates. These are the following:
40   * </p>
41   * <ul>
42   * <li>A name pattern for the threads created by this factory can be specified.
43   * This is often useful if an application uses multiple executor services for
44   * different purposes. If the names of the threads used by these services have
45   * meaningful names, log output or exception traces can be much easier to read.
46   * Naming patterns are <em>format strings</em> as used by the {@code
47   * String.format()} method. The string can contain the place holder {@code %d}
48   * which will be replaced by the number of the current thread ({@code
49   * ThreadFactoryImpl} keeps a counter of the threads it has already created).
50   * For instance, the naming pattern {@code "My %d. worker thread"} will result
51   * in thread names like {@code "My 1. worker thread"}, {@code
52   * "My 2. worker thread"} and so on.</li>
53   * <li>A flag whether the threads created by this factory should be daemon
54   * threads. This can impact the exit behavior of the current Java application
55   * because the JVM shuts down if there are only daemon threads running.</li>
56   * <li>The priority of the thread. Here an integer value can be provided. The
57   * {@code java.lang.Thread} class defines constants for valid ranges of priority
58   * values.</li>
59   * <li>The {@code UncaughtExceptionHandler} for the thread. This handler is
60   * called if an uncaught exception occurs within the thread.</li>
61   * </ul>
62   * <p>
63   * {@code BasicThreadFactory} wraps another thread factory which actually
64   * creates new threads. The configuration options are set on the threads created
65   * by the wrapped thread factory. On construction time the factory to be wrapped
66   * can be specified. If none is provided, a default {@code ThreadFactory} is
67   * used.
68   * </p>
69   * <p>
70   * Instances of {@code BasicThreadFactory} are not created directly, but the
71   * nested {@code Builder} class is used for this purpose. Using the builder only
72   * the configuration options an application is interested in need to be set. The
73   * following example shows how a {@code BasicThreadFactory} is created and
74   * installed in an {@code ExecutorService}:
75   * </p>
76   *
77   * <pre>
78   * // Create a factory that produces daemon threads with a naming pattern and
79   * // a priority
80   * BasicThreadFactory factory = new BasicThreadFactory.Builder()
81   *     .namingPattern(&quot;workerthread-%d&quot;)
82   *     .daemon(true)
83   *     .priority(Thread.MAX_PRIORITY)
84   *     .build();
85   * // Create an executor service for single-threaded execution
86   * ExecutorService exec = Executors.newSingleThreadExecutor(factory);
87   * </pre>
88   *
89   * @since 3.0
90   */
91  public class BasicThreadFactory implements ThreadFactory {
92      /** A counter for the threads created by this factory. */
93      private final AtomicLong threadCounter;
94  
95      /** Stores the wrapped factory. */
96      private final ThreadFactory wrappedFactory;
97  
98      /** Stores the uncaught exception handler. */
99      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 }