    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 * <p>
    030 * A {@link ThreadFactory} is used for instance by an {@link ExecutorService} to
    031 * create the threads it uses for executing tasks. In many cases users do not
    032 * have to care about a {@link ThreadFactory} because the default one used by an
    033 * {@link ExecutorService} will do. However, if there are special requirements
    034 * for the threads, a custom {@link ThreadFactory} has to be created.
    035 * </p>
    036 * <p>
    037 * This class provides some frequently needed configuration options for the
    038 * threads it creates. These are the following:
    039 * </p>
    040 * <ul>
    041 * <li>A name pattern for the threads created by this factory can be specified.
    042 * This is often useful if an application uses multiple executor services for
    043 * different purposes. If the names of the threads used by these services have
    044 * meaningful names, log output or exception traces can be much easier to read.
    045 * Naming patterns are <em>format strings</em> as used by the {@code
    046 * String.format()} method. The string can contain the place holder {@code %d}
    047 * which will be replaced by the number of the current thread ({@code
    048 * ThreadFactoryImpl} keeps a counter of the threads it has already created).
    049 * For instance, the naming pattern {@code "My %d. worker thread"} will result
    050 * in thread names like {@code "My 1. worker thread"}, {@code
    051 * "My 2. worker thread"} and so on.</li>
    052 * <li>A flag whether the threads created by this factory should be daemon
    053 * threads. This can impact the exit behavior of the current Java application
    054 * because the JVM shuts down if there are only daemon threads running.</li>
    055 * <li>The priority of the thread. Here an integer value can be provided. The
    056 * {@link Thread} class defines constants for valid ranges of priority
    057 * values.</li>
    058 * <li>The {@link UncaughtExceptionHandler} for the thread. This handler is
    059 * called if an uncaught exception occurs within the thread.</li>
    060 * </ul>
    061 * <p>
    062 * {@link BasicThreadFactory} wraps another thread factory which actually
    063 * creates new threads. The configuration options are set on the threads created
    064 * by the wrapped thread factory. On construction time the factory to be wrapped
    065 * can be specified. If none is provided, a default {@link ThreadFactory} is
    066 * used.
    067 * </p>
    068 * <p>
    069 * Instances of {@link BasicThreadFactory} are not created directly, but the
    070 * nested {@link Builder} class is used for this purpose. Using the builder only
    071 * the configuration options an application is interested in need to be set. The
    072 * following example shows how a {@link BasicThreadFactory} is created and
    073 * installed in an {@link ExecutorService}:
    074 * </p>
    075 *
    076 * <pre>
    077 * // Create a factory that produces daemon threads with a naming pattern and
    078 * // a priority
    079 * BasicThreadFactory factory = new BasicThreadFactory.Builder()
    080 *     .namingPattern(&quot;workerthread-%d&quot;)
    081 *     .daemon(true)
    082 *     .priority(Thread.MAX_PRIORITY)
    083 *     .build();
    084 * // Create an executor service for single-threaded execution
    085 * ExecutorService exec = Executors.newSingleThreadExecutor(factory);
    086 * </pre>
    087 *
    088 * @since 3.0
    089 */
    090public class BasicThreadFactory implements ThreadFactory {
    091
    092    /**
    093     * A <em>builder</em> class for creating instances of {@code
    094     * BasicThreadFactory}.
    095     * <p>
    096     * Using this builder class instances of {@link BasicThreadFactory} can be
    097     * created and initialized. The class provides methods that correspond to
    098     * the configuration options supported by {@link BasicThreadFactory}. Method
    099     * chaining is supported. Refer to the documentation of {@code
    100     * BasicThreadFactory} for a usage example.
    101     * </p>
    102     */
    103    public static class Builder implements org.apache.commons.lang3.builder.Builder<BasicThreadFactory> {
    104
    105        /** The wrapped factory. */
    106        private ThreadFactory factory;
    107
    108        /** The uncaught exception handler. */
    109        private Thread.UncaughtExceptionHandler exceptionHandler;
    110
    111        /** The naming pattern. */
    112        private String namingPattern;
    113
    114        /** The priority. */
    115        private Integer priority;
    116
    117        /** The daemon flag. */
    118        private Boolean daemon;
    119
    120        /**
    121         * Constructs a new instance.
    122         */
    123        public Builder() {
    124            // empty
    125        }
    126
    127        /**
    128         * Creates a new {@link BasicThreadFactory} with all configuration
    129         * options that have been specified by calling methods on this builder.
    130         * After creating the factory {@link #reset()} is called.
    131         *
    132         * @return the new {@link BasicThreadFactory}
    133         */
    134        @Override
    135        public BasicThreadFactory build() {
    136            final BasicThreadFactory factory = new BasicThreadFactory(this);
    137            reset();
    138            return factory;
    139        }
    140
    141        /**
    142         * Sets the daemon flag for the new {@link BasicThreadFactory}. If this
    143         * flag is set to <b>true</b> the new thread factory will create daemon
    144         * threads.
    145         *
    146         * @param daemon the value of the daemon flag
    147         * @return a reference to this {@link Builder}
    148         */
    149        public Builder daemon(final boolean daemon) {
    150            this.daemon = Boolean.valueOf(daemon);
    151            return this;
    152        }
    153
    154        /**
    155         * Sets the naming pattern to be used by the new {@code
    156         * BasicThreadFactory}.
    157         *
    158         * @param namingPattern the naming pattern (must not be <b>null</b>)
    159         * @return a reference to this {@link Builder}
    160         * @throws NullPointerException if the naming pattern is <b>null</b>
    161         */
    162        public Builder namingPattern(final String namingPattern) {
    163            this.namingPattern = Objects.requireNonNull(namingPattern, "pattern");
    164            return this;
    165        }
    166
    167        /**
    168         * Sets the priority for the threads created by the new {@code
    169         * BasicThreadFactory}.
    170         *
    171         * @param priority the priority
    172         * @return a reference to this {@link Builder}
    173         */
    174        public Builder priority(final int priority) {
    175            this.priority = Integer.valueOf(priority);
    176            return this;
    177        }
    178
    179        /**
    180         * Resets this builder. All configuration options are set to default
    181         * values. Note: If the {@link #build()} method was called, it is not
    182         * necessary to call {@code reset()} explicitly because this is done
    183         * automatically.
    184         */
    185        public void reset() {
    186            factory = null;
    187            exceptionHandler = null;
    188            namingPattern = null;
    189            priority = null;
    190            daemon = null;
    191        }
    192
    193        /**
    194         * Sets the uncaught exception handler for the threads created by the
    195         * new {@link BasicThreadFactory}.
    196         *
    197         * @param exceptionHandler the {@link UncaughtExceptionHandler} (must not be
    198         * <b>null</b>)
    199         * @return a reference to this {@link Builder}
    200         * @throws NullPointerException if the exception handler is <b>null</b>
    201         */
    202        public Builder uncaughtExceptionHandler(
    203                final Thread.UncaughtExceptionHandler exceptionHandler) {
    204            this.exceptionHandler = Objects.requireNonNull(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            this.factory = Objects.requireNonNull(factory, "factory");
    220            return this;
    221        }
    222    }
    223
    224    /** A counter for the threads created by this factory. */
    225    private final AtomicLong threadCounter;
    226
    227    /** Stores the wrapped factory. */
    228    private final ThreadFactory wrappedFactory;
    229
    230    /** Stores the uncaught exception handler. */
    231    private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
    232
    233    /** Stores the naming pattern for newly created threads. */
    234    private final String namingPattern;
    235
    236    /** Stores the priority. */
    237    private final Integer priority;
    238
    239    /** Stores the daemon status flag. */
    240    private final Boolean daemon;
    241
    242    /**
    243     * Creates a new instance of {@link ThreadFactory} and configures it
    244     * from the specified {@link Builder} object.
    245     *
    246     * @param builder the {@link Builder} object
    247     */
    248    private BasicThreadFactory(final Builder builder) {
    249        wrappedFactory = builder.factory != null ? builder.factory : Executors.defaultThreadFactory();
    250        namingPattern = builder.namingPattern;
    251        priority = builder.priority;
    252        daemon = builder.daemon;
    253        uncaughtExceptionHandler = builder.exceptionHandler;
    254        threadCounter = new AtomicLong();
    255    }
    256
    257    /**
    258     * Gets the daemon flag. This flag determines whether newly created
    259     * threads should be daemon threads. If <b>true</b>, this factory object
    260     * calls {@code setDaemon(true)} on the newly created threads. Result can be
    261     * <b>null</b> if no daemon flag was provided at creation time.
    262     *
    263     * @return the daemon flag
    264     */
    265    public final Boolean getDaemonFlag() {
    266        return daemon;
    267    }
    268
    269    /**
    270     * Gets the naming pattern for naming newly created threads. Result can
    271     * be <b>null</b> if no naming pattern was provided.
    272     *
    273     * @return the naming pattern
    274     */
    275    public final String getNamingPattern() {
    276        return namingPattern;
    277    }
    278
    279    /**
    280     * Gets the priority of the threads created by this factory. Result can
    281     * be <b>null</b> if no priority was specified.
    282     *
    283     * @return the priority for newly created threads
    284     */
    285    public final Integer getPriority() {
    286        return priority;
    287    }
    288
    289    /**
    290     * Gets the number of threads this factory has already created. This
    291     * class maintains an internal counter that is incremented each time the
    292     * {@link #newThread(Runnable)} method is invoked.
    293     *
    294     * @return the number of threads created by this factory
    295     */
    296    public long getThreadCount() {
    297        return threadCounter.get();
    298    }
    299
    300    /**
    301     * Gets the {@link UncaughtExceptionHandler} for the threads created by
    302     * this factory. Result can be <b>null</b> if no handler was provided.
    303     *
    304     * @return the {@link UncaughtExceptionHandler}
    305     */
    306    public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
    307        return uncaughtExceptionHandler;
    308    }
    309
    310    /**
    311     * Gets the wrapped {@link ThreadFactory}. This factory is used for
    312     * actually creating threads. This method never returns <b>null</b>. If no
    313     * {@link ThreadFactory} was passed when this object was created, a default
    314     * thread factory is returned.
    315     *
    316     * @return the wrapped {@link ThreadFactory}
    317     */
    318    public final ThreadFactory getWrappedFactory() {
    319        return wrappedFactory;
    320    }
    321
    322    /**
    323     * Initializes the specified thread. This method is called by
    324     * {@link #newThread(Runnable)} after a new thread has been obtained from
    325     * the wrapped thread factory. It initializes the thread according to the
    326     * options set for this factory.
    327     *
    328     * @param thread the thread to be initialized
    329     */
    330    private void initializeThread(final Thread thread) {
    331        if (getNamingPattern() != null) {
    332            final Long count = Long.valueOf(threadCounter.incrementAndGet());
    333            thread.setName(String.format(getNamingPattern(), count));
    334        }
    335        if (getUncaughtExceptionHandler() != null) {
    336            thread.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
    337        }
    338        if (getPriority() != null) {
    339            thread.setPriority(getPriority().intValue());
    340        }
    341        if (getDaemonFlag() != null) {
    342            thread.setDaemon(getDaemonFlag().booleanValue());
    343        }
    344    }
    345
    346    /**
    347     * Creates a new thread. This implementation delegates to the wrapped
    348     * factory for creating the thread. Then, on the newly created thread the
    349     * corresponding configuration options are set.
    350     *
    351     * @param runnable the {@link Runnable} to be executed by the new thread
    352     * @return the newly created thread
    353     */
    354    @Override
    355    public Thread newThread(final Runnable runnable) {
    356        final Thread thread = getWrappedFactory().newThread(runnable);
    357        initializeThread(thread);
    358        return thread;
    359    }
    360}