    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}