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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   * @version $Id: BasicThreadFactory.java 1583482 2014-03-31 22:54:57Z niallp $
89   */
90  public class BasicThreadFactory implements ThreadFactory {
91      /** A counter for the threads created by this factory. */
92      private final AtomicLong threadCounter;
93  
94      /** Stores the wrapped factory. */
95      private final ThreadFactory wrappedFactory;
96  
97      /** Stores the uncaught exception handler. */
98      private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
99  
100     /** Stores the naming pattern for newly created threads. */
101     private final String namingPattern;
102 
103     /** Stores the priority. */
104     private final Integer priority;
105 
106     /** Stores the daemon status flag. */
107     private final Boolean daemonFlag;
108 
109     /**
110      * Creates a new instance of {@code ThreadFactoryImpl} and configures it
111      * from the specified {@code Builder} object.
112      *
113      * @param builder the {@code Builder} object
114      */
115     private BasicThreadFactory(final Builder builder) {
116         if (builder.wrappedFactory == null) {
117             wrappedFactory = Executors.defaultThreadFactory();
118         } else {
119             wrappedFactory = builder.wrappedFactory;
120         }
121 
122         namingPattern = builder.namingPattern;
123         priority = builder.priority;
124         daemonFlag = builder.daemonFlag;
125         uncaughtExceptionHandler = builder.exceptionHandler;
126 
127         threadCounter = new AtomicLong();
128     }
129 
130     /**
131      * Returns the wrapped {@code ThreadFactory}. This factory is used for
132      * actually creating threads. This method never returns <b>null</b>. If no
133      * {@code ThreadFactory} was passed when this object was created, a default
134      * thread factory is returned.
135      *
136      * @return the wrapped {@code ThreadFactory}
137      */
138     public final ThreadFactory getWrappedFactory() {
139         return wrappedFactory;
140     }
141 
142     /**
143      * Returns the naming pattern for naming newly created threads. Result can
144      * be <b>null</b> if no naming pattern was provided.
145      *
146      * @return the naming pattern
147      */
148     public final String getNamingPattern() {
149         return namingPattern;
150     }
151 
152     /**
153      * Returns the daemon flag. This flag determines whether newly created
154      * threads should be daemon threads. If <b>true</b>, this factory object
155      * calls {@code setDaemon(true)} on the newly created threads. Result can be
156      * <b>null</b> if no daemon flag was provided at creation time.
157      *
158      * @return the daemon flag
159      */
160     public final Boolean getDaemonFlag() {
161         return daemonFlag;
162     }
163 
164     /**
165      * Returns the priority of the threads created by this factory. Result can
166      * be <b>null</b> if no priority was specified.
167      *
168      * @return the priority for newly created threads
169      */
170     public final Integer getPriority() {
171         return priority;
172     }
173 
174     /**
175      * Returns the {@code UncaughtExceptionHandler} for the threads created by
176      * this factory. Result can be <b>null</b> if no handler was provided.
177      *
178      * @return the {@code UncaughtExceptionHandler}
179      */
180     public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
181         return uncaughtExceptionHandler;
182     }
183 
184     /**
185      * Returns the number of threads this factory has already created. This
186      * class maintains an internal counter that is incremented each time the
187      * {@link #newThread(Runnable)} method is invoked.
188      *
189      * @return the number of threads created by this factory
190      */
191     public long getThreadCount() {
192         return threadCounter.get();
193     }
194 
195     /**
196      * Creates a new thread. This implementation delegates to the wrapped
197      * factory for creating the thread. Then, on the newly created thread the
198      * corresponding configuration options are set.
199      *
200      * @param r the {@code Runnable} to be executed by the new thread
201      * @return the newly created thread
202      */
203     @Override
204     public Thread newThread(final Runnable r) {
205         final Thread t = getWrappedFactory().newThread(r);
206         initializeThread(t);
207 
208         return t;
209     }
210 
211     /**
212      * Initializes the specified thread. This method is called by
213      * {@link #newThread(Runnable)} after a new thread has been obtained from
214      * the wrapped thread factory. It initializes the thread according to the
215      * options set for this factory.
216      *
217      * @param t the thread to be initialized
218      */
219     private void initializeThread(final Thread t) {
220 
221         if (getNamingPattern() != null) {
222             final Long count = Long.valueOf(threadCounter.incrementAndGet());
223             t.setName(String.format(getNamingPattern(), count));
224         }
225 
226         if (getUncaughtExceptionHandler() != null) {
227             t.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
228         }
229 
230         if (getPriority() != null) {
231             t.setPriority(getPriority().intValue());
232         }
233 
234         if (getDaemonFlag() != null) {
235             t.setDaemon(getDaemonFlag().booleanValue());
236         }
237     }
238 
239     /**
240      * <p>
241      * A <em>builder</em> class for creating instances of {@code
242      * BasicThreadFactory}.
243      * </p>
244      * <p>
245      * Using this builder class instances of {@code BasicThreadFactory} can be
246      * created and initialized. The class provides methods that correspond to
247      * the configuration options supported by {@code BasicThreadFactory}. Method
248      * chaining is supported. Refer to the documentation of {@code
249      * BasicThreadFactory} for a usage example.
250      * </p>
251      *
252      * @version $Id: BasicThreadFactory.java 1583482 2014-03-31 22:54:57Z niallp $
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             if (factory == null) {
284                 throw new NullPointerException(
285                         "Wrapped ThreadFactory must not be null!");
286             }
287 
288             wrappedFactory = factory;
289             return this;
290         }
291 
292         /**
293          * Sets the naming pattern to be used by the new {@code
294          * BasicThreadFactory}.
295          *
296          * @param pattern the naming pattern (must not be <b>null</b>)
297          * @return a reference to this {@code Builder}
298          * @throws NullPointerException if the naming pattern is <b>null</b>
299          */
300         public Builder namingPattern(final String pattern) {
301             if (pattern == null) {
302                 throw new NullPointerException(
303                         "Naming pattern must not be null!");
304             }
305 
306             namingPattern = pattern;
307             return this;
308         }
309 
310         /**
311          * Sets the daemon flag for the new {@code BasicThreadFactory}. If this
312          * flag is set to <b>true</b> the new thread factory will create daemon
313          * threads.
314          *
315          * @param f the value of the daemon flag
316          * @return a reference to this {@code Builder}
317          */
318         public Builder daemon(final boolean f) {
319             daemonFlag = Boolean.valueOf(f);
320             return this;
321         }
322 
323         /**
324          * Sets the priority for the threads created by the new {@code
325          * BasicThreadFactory}.
326          *
327          * @param prio the priority
328          * @return a reference to this {@code Builder}
329          */
330         public Builder priority(final int prio) {
331             priority = Integer.valueOf(prio);
332             return this;
333         }
334 
335         /**
336          * Sets the uncaught exception handler for the threads created by the
337          * new {@code BasicThreadFactory}.
338          *
339          * @param handler the {@code UncaughtExceptionHandler} (must not be
340          * <b>null</b>)
341          * @return a reference to this {@code Builder}
342          * @throws NullPointerException if the exception handler is <b>null</b>
343          */
344         public Builder uncaughtExceptionHandler(
345                 final Thread.UncaughtExceptionHandler handler) {
346             if (handler == null) {
347                 throw new NullPointerException(
348                         "Uncaught exception handler must not be null!");
349             }
350 
351             exceptionHandler = handler;
352             return this;
353         }
354 
355         /**
356          * Resets this builder. All configuration options are set to default
357          * values. Note: If the {@link #build()} method was called, it is not
358          * necessary to call {@code reset()} explicitly because this is done
359          * automatically.
360          */
361         public void reset() {
362             wrappedFactory = null;
363             exceptionHandler = null;
364             namingPattern = null;
365             priority = null;
366             daemonFlag = null;
367         }
368 
369         /**
370          * Creates a new {@code BasicThreadFactory} with all configuration
371          * options that have been specified by calling methods on this builder.
372          * After creating the factory {@link #reset()} is called.
373          *
374          * @return the new {@code BasicThreadFactory}
375          */
376         @Override
377         public BasicThreadFactory build() {
378             final BasicThreadFactory factory = new BasicThreadFactory(this);
379             reset();
380             return factory;
381         }
382     }
383 }