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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  /**
24   * <p>
25   * An implementation of the {@code ThreadFactory} interface that provides some
26   * configuration options for the threads it creates.
27   * </p>
28   * <p>
29   * A {@code ThreadFactory} is used for instance by an {@code ExecutorService} to
30   * create the threads it uses for executing tasks. In many cases users do not
31   * have to care about a {@code ThreadFactory} because the default one used by an
32   * {@code ExecutorService} will do. However, if there are special requirements
33   * for the threads, a custom {@code ThreadFactory} has to be created.
34   * </p>
35   * <p>
36   * This class provides some frequently needed configuration options for the
37   * threads it creates. These are the following:
38   * </p>
39   * <ul>
40   * <li>A name pattern for the threads created by this factory can be specified.
41   * This is often useful if an application uses multiple executor services for
42   * different purposes. If the names of the threads used by these services have
43   * meaningful names, log output or exception traces can be much easier to read.
44   * Naming patterns are <em>format strings</em> as used by the {@code
45   * String.format()} method. The string can contain the place holder {@code %d}
46   * which will be replaced by the number of the current thread ({@code
47   * ThreadFactoryImpl} keeps a counter of the threads it has already created).
48   * For instance, the naming pattern {@code "My %d. worker thread"} will result
49   * in thread names like {@code "My 1. worker thread"}, {@code
50   * "My 2. worker thread"} and so on.</li>
51   * <li>A flag whether the threads created by this factory should be daemon
52   * threads. This can impact the exit behavior of the current Java application
53   * because the JVM shuts down if there are only daemon threads running.</li>
54   * <li>The priority of the thread. Here an integer value can be provided. The
55   * {@code java.lang.Thread} class defines constants for valid ranges of priority
56   * values.</li>
57   * <li>The {@code UncaughtExceptionHandler} for the thread. This handler is
58   * called if an uncaught exception occurs within the thread.</li>
59   * </ul>
60   * <p>
61   * {@code BasicThreadFactory} wraps another thread factory which actually
62   * creates new threads. The configuration options are set on the threads created
63   * by the wrapped thread factory. On construction time the factory to be wrapped
64   * can be specified. If none is provided, a default {@code ThreadFactory} is
65   * used.
66   * </p>
67   * <p>
68   * Instances of {@code BasicThreadFactory} are not created directly, but the
69   * nested {@code Builder} class is used for this purpose. Using the builder only
70   * the configuration options an application is interested in need to be set. The
71   * following example shows how a {@code BasicThreadFactory} is created and
72   * installed in an {@code ExecutorService}:
73   * </p>
74   *
75   * <pre>
76   * // Create a factory that produces daemon threads with a naming pattern and
77   * // a priority
78   * BasicThreadFactory factory = new BasicThreadFactory.Builder()
79   *     .namingPattern(&quot;workerthread-%d&quot;)
80   *     .daemon(true)
81   *     .priority(Thread.MAX_PRIORITY)
82   *     .build();
83   * // Create an executor service for single-threaded execution
84   * ExecutorService exec = Executors.newSingleThreadExecutor(factory);
85   * </pre>
86   *
87   * @since 3.0
88   */
89  public class BasicThreadFactory implements ThreadFactory {
90      /** A counter for the threads created by this factory. */
91      private final AtomicLong threadCounter;
92  
93      /** Stores the wrapped factory. */
94      private final ThreadFactory wrappedFactory;
95  
96      /** Stores the uncaught exception handler. */
97      private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
98  
99      /** Stores the naming pattern for newly created threads. */
100     private final String namingPattern;
101 
102     /** Stores the priority. */
103     private final Integer priority;
104 
105     /** Stores the daemon status flag. */
106     private final Boolean daemonFlag;
107 
108     /**
109      * Creates a new instance of {@code ThreadFactoryImpl} and configures it
110      * from the specified {@code Builder} object.
111      *
112      * @param builder the {@code Builder} object
113      */
114     private BasicThreadFactory(final Builder builder) {
115         if (builder.wrappedFactory == null) {
116             wrappedFactory = Executors.defaultThreadFactory();
117         } else {
118             wrappedFactory = builder.wrappedFactory;
119         }
120 
121         namingPattern = builder.namingPattern;
122         priority = builder.priority;
123         daemonFlag = builder.daemonFlag;
124         uncaughtExceptionHandler = builder.exceptionHandler;
125 
126         threadCounter = new AtomicLong();
127     }
128 
129     /**
130      * Returns the wrapped {@code ThreadFactory}. This factory is used for
131      * actually creating threads. This method never returns <b>null</b>. If no
132      * {@code ThreadFactory} was passed when this object was created, a default
133      * thread factory is returned.
134      *
135      * @return the wrapped {@code ThreadFactory}
136      */
137     public final ThreadFactory getWrappedFactory() {
138         return wrappedFactory;
139     }
140 
141     /**
142      * Returns the naming pattern for naming newly created threads. Result can
143      * be <b>null</b> if no naming pattern was provided.
144      *
145      * @return the naming pattern
146      */
147     public final String getNamingPattern() {
148         return namingPattern;
149     }
150 
151     /**
152      * Returns the daemon flag. This flag determines whether newly created
153      * threads should be daemon threads. If <b>true</b>, this factory object
154      * calls {@code setDaemon(true)} on the newly created threads. Result can be
155      * <b>null</b> if no daemon flag was provided at creation time.
156      *
157      * @return the daemon flag
158      */
159     public final Boolean getDaemonFlag() {
160         return daemonFlag;
161     }
162 
163     /**
164      * Returns the priority of the threads created by this factory. Result can
165      * be <b>null</b> if no priority was specified.
166      *
167      * @return the priority for newly created threads
168      */
169     public final Integer getPriority() {
170         return priority;
171     }
172 
173     /**
174      * Returns the {@code UncaughtExceptionHandler} for the threads created by
175      * this factory. Result can be <b>null</b> if no handler was provided.
176      *
177      * @return the {@code UncaughtExceptionHandler}
178      */
179     public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
180         return uncaughtExceptionHandler;
181     }
182 
183     /**
184      * Returns the number of threads this factory has already created. This
185      * class maintains an internal counter that is incremented each time the
186      * {@link #newThread(Runnable)} method is invoked.
187      *
188      * @return the number of threads created by this factory
189      */
190     public long getThreadCount() {
191         return threadCounter.get();
192     }
193 
194     /**
195      * Creates a new thread. This implementation delegates to the wrapped
196      * factory for creating the thread. Then, on the newly created thread the
197      * corresponding configuration options are set.
198      *
199      * @param r the {@code Runnable} to be executed by the new thread
200      * @return the newly created thread
201      */
202     @Override
203     public Thread newThread(final Runnable r) {
204         final Thread t = getWrappedFactory().newThread(r);
205         initializeThread(t);
206 
207         return t;
208     }
209 
210     /**
211      * Initializes the specified thread. This method is called by
212      * {@link #newThread(Runnable)} after a new thread has been obtained from
213      * the wrapped thread factory. It initializes the thread according to the
214      * options set for this factory.
215      *
216      * @param t the thread to be initialized
217      */
218     private void initializeThread(final Thread t) {
219 
220         if (getNamingPattern() != null) {
221             final Long count = Long.valueOf(threadCounter.incrementAndGet());
222             t.setName(String.format(getNamingPattern(), count));
223         }
224 
225         if (getUncaughtExceptionHandler() != null) {
226             t.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
227         }
228 
229         if (getPriority() != null) {
230             t.setPriority(getPriority().intValue());
231         }
232 
233         if (getDaemonFlag() != null) {
234             t.setDaemon(getDaemonFlag().booleanValue());
235         }
236     }
237 
238     /**
239      * <p>
240      * A <em>builder</em> class for creating instances of {@code
241      * BasicThreadFactory}.
242      * </p>
243      * <p>
244      * Using this builder class instances of {@code BasicThreadFactory} can be
245      * created and initialized. The class provides methods that correspond to
246      * the configuration options supported by {@code BasicThreadFactory}. Method
247      * chaining is supported. Refer to the documentation of {@code
248      * BasicThreadFactory} for a usage example.
249      * </p>
250      *
251      */
252     public static class Builder 
253         implements org.apache.commons.lang3.builder.Builder<BasicThreadFactory> {
254         
255         /** The wrapped factory. */
256         private ThreadFactory wrappedFactory;
257 
258         /** The uncaught exception handler. */
259         private Thread.UncaughtExceptionHandler exceptionHandler;
260 
261         /** The naming pattern. */
262         private String namingPattern;
263 
264         /** The priority. */
265         private Integer priority;
266 
267         /** The daemon flag. */
268         private Boolean daemonFlag;
269 
270         /**
271          * Sets the {@code ThreadFactory} to be wrapped by the new {@code
272          * BasicThreadFactory}.
273          *
274          * @param factory the wrapped {@code ThreadFactory} (must not be
275          * <b>null</b>)
276          * @return a reference to this {@code Builder}
277          * @throws NullPointerException if the passed in {@code ThreadFactory}
278          * is <b>null</b>
279          */
280         public Builder wrappedFactory(final ThreadFactory factory) {
281             if (factory == null) {
282                 throw new NullPointerException(
283                         "Wrapped ThreadFactory must not be null!");
284             }
285 
286             wrappedFactory = factory;
287             return this;
288         }
289 
290         /**
291          * Sets the naming pattern to be used by the new {@code
292          * BasicThreadFactory}.
293          *
294          * @param pattern the naming pattern (must not be <b>null</b>)
295          * @return a reference to this {@code Builder}
296          * @throws NullPointerException if the naming pattern is <b>null</b>
297          */
298         public Builder namingPattern(final String pattern) {
299             if (pattern == null) {
300                 throw new NullPointerException(
301                         "Naming pattern must not be null!");
302             }
303 
304             namingPattern = pattern;
305             return this;
306         }
307 
308         /**
309          * Sets the daemon flag for the new {@code BasicThreadFactory}. If this
310          * flag is set to <b>true</b> the new thread factory will create daemon
311          * threads.
312          *
313          * @param f the value of the daemon flag
314          * @return a reference to this {@code Builder}
315          */
316         public Builder daemon(final boolean f) {
317             daemonFlag = Boolean.valueOf(f);
318             return this;
319         }
320 
321         /**
322          * Sets the priority for the threads created by the new {@code
323          * BasicThreadFactory}.
324          *
325          * @param prio the priority
326          * @return a reference to this {@code Builder}
327          */
328         public Builder priority(final int prio) {
329             priority = Integer.valueOf(prio);
330             return this;
331         }
332 
333         /**
334          * Sets the uncaught exception handler for the threads created by the
335          * new {@code BasicThreadFactory}.
336          *
337          * @param handler the {@code UncaughtExceptionHandler} (must not be
338          * <b>null</b>)
339          * @return a reference to this {@code Builder}
340          * @throws NullPointerException if the exception handler is <b>null</b>
341          */
342         public Builder uncaughtExceptionHandler(
343                 final Thread.UncaughtExceptionHandler handler) {
344             if (handler == null) {
345                 throw new NullPointerException(
346                         "Uncaught exception handler must not be null!");
347             }
348 
349             exceptionHandler = handler;
350             return this;
351         }
352 
353         /**
354          * Resets this builder. All configuration options are set to default
355          * values. Note: If the {@link #build()} method was called, it is not
356          * necessary to call {@code reset()} explicitly because this is done
357          * automatically.
358          */
359         public void reset() {
360             wrappedFactory = null;
361             exceptionHandler = null;
362             namingPattern = null;
363             priority = null;
364             daemonFlag = null;
365         }
366 
367         /**
368          * Creates a new {@code BasicThreadFactory} with all configuration
369          * options that have been specified by calling methods on this builder.
370          * After creating the factory {@link #reset()} is called.
371          *
372          * @return the new {@code BasicThreadFactory}
373          */
374         @Override
375         public BasicThreadFactory build() {
376             final BasicThreadFactory factory = new BasicThreadFactory(this);
377             reset();
378             return factory;
379         }
380     }
381 }