/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.lang3.concurrent;
  
  import java.lang.Thread.UncaughtExceptionHandler;
  import java.util.Objects;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * An implementation of the {@link ThreadFactory} interface that provides some
   * configuration options for the threads it creates.
   * <p>
   * A {@link ThreadFactory} is used for instance by an {@link ExecutorService} to
   * create the threads it uses for executing tasks. In many cases users do not
   * have to care about a {@link ThreadFactory} because the default one used by an
   * {@link ExecutorService} will do. However, if there are special requirements
   * for the threads, a custom {@link ThreadFactory} has to be created.
   * </p>
   * <p>
   * This class provides some frequently needed configuration options for the
   * threads it creates. These are the following:
   * </p>
   * <ul>
   * <li>A name pattern for the threads created by this factory can be specified.
   * This is often useful if an application uses multiple executor services for
   * different purposes. If the names of the threads used by these services have
   * meaningful names, log output or exception traces can be much easier to read.
   * Naming patterns are <em>format strings</em> as used by the {@code
   * String.format()} method. The string can contain the place holder {@code %d}
   * which will be replaced by the number of the current thread ({@code
   * ThreadFactoryImpl} keeps a counter of the threads it has already created).
   * For instance, the naming pattern {@code "My %d. worker thread"} will result
   * in thread names like {@code "My 1. worker thread"}, {@code
   * "My 2. worker thread"} and so on.</li>
   * <li>A flag whether the threads created by this factory should be daemon
   * threads. This can impact the exit behavior of the current Java application
   * because the JVM shuts down if there are only daemon threads running.</li>
   * <li>The priority of the thread. Here an integer value can be provided. The
   * {@link Thread} class defines constants for valid ranges of priority
   * values.</li>
   * <li>The {@link UncaughtExceptionHandler} for the thread. This handler is
   * called if an uncaught exception occurs within the thread.</li>
   * </ul>
   * <p>
   * {@link BasicThreadFactory} wraps another thread factory which actually
   * creates new threads. The configuration options are set on the threads created
   * by the wrapped thread factory. On construction time the factory to be wrapped
   * can be specified. If none is provided, a default {@link ThreadFactory} is
   * used.
   * </p>
   * <p>
   * Instances of {@link BasicThreadFactory} are not created directly, but the
   * nested {@link Builder} class is used for this purpose. Using the builder only
   * the configuration options an application is interested in need to be set. The
   * following example shows how a {@link BasicThreadFactory} is created and
   * installed in an {@link ExecutorService}:
   * </p>
   *
   * <pre>
   * // Create a factory that produces daemon threads with a naming pattern and
   * // a priority
   * BasicThreadFactory factory = new BasicThreadFactory.Builder()
   *     .namingPattern(&quot;workerthread-%d&quot;)
   *     .daemon(true)
   *     .priority(Thread.MAX_PRIORITY)
   *     .build();
   * // Create an executor service for single-threaded execution
   * ExecutorService exec = Executors.newSingleThreadExecutor(factory);
   * </pre>
   *
   * @since 3.0
   */
  public class BasicThreadFactory implements ThreadFactory {
  
      /**
       * A <em>builder</em> class for creating instances of {@code
       * BasicThreadFactory}.
       * <p>
       * Using this builder class instances of {@link BasicThreadFactory} can be
       * created and initialized. The class provides methods that correspond to
       * the configuration options supported by {@link BasicThreadFactory}. Method
       * chaining is supported. Refer to the documentation of {@code
      * BasicThreadFactory} for a usage example.
      * </p>
      */
     public static class Builder implements org.apache.commons.lang3.builder.Builder<BasicThreadFactory> {
 
         /** The wrapped factory. */
         private ThreadFactory factory;
 
         /** The uncaught exception handler. */
         private Thread.UncaughtExceptionHandler exceptionHandler;
 
         /** The naming pattern. */
         private String namingPattern;
 
         /** The priority. */
         private Integer priority;
 
         /** The daemon flag. */
         private Boolean daemon;
 
         /**
          * Constructs a new instance.
          */
         public Builder() {
             // empty
         }
 
         /**
          * Creates a new {@link BasicThreadFactory} with all configuration
          * options that have been specified by calling methods on this builder.
          * After creating the factory {@link #reset()} is called.
          *
          * @return the new {@link BasicThreadFactory}
          */
         @Override
         public BasicThreadFactory build() {
             final BasicThreadFactory factory = new BasicThreadFactory(this);
             reset();
             return factory;
         }
 
         /**
          * Sets the daemon flag for the new {@link BasicThreadFactory}. If this
          * flag is set to <b>true</b> the new thread factory will create daemon
          * threads.
          *
          * @param daemon the value of the daemon flag
          * @return a reference to this {@link Builder}
          */
         public Builder daemon(final boolean daemon) {
             this.daemon = Boolean.valueOf(daemon);
             return this;
         }
 
         /**
          * Sets the naming pattern to be used by the new {@code
          * BasicThreadFactory}.
          *
          * @param namingPattern the naming pattern (must not be <b>null</b>)
          * @return a reference to this {@link Builder}
          * @throws NullPointerException if the naming pattern is <b>null</b>
          */
         public Builder namingPattern(final String namingPattern) {
             this.namingPattern = Objects.requireNonNull(namingPattern, "pattern");
             return this;
         }
 
         /**
          * Sets the priority for the threads created by the new {@code
          * BasicThreadFactory}.
          *
          * @param priority the priority
          * @return a reference to this {@link Builder}
          */
         public Builder priority(final int priority) {
             this.priority = Integer.valueOf(priority);
             return this;
         }
 
         /**
          * Resets this builder. All configuration options are set to default
          * values. Note: If the {@link #build()} method was called, it is not
          * necessary to call {@code reset()} explicitly because this is done
          * automatically.
          */
         public void reset() {
             factory = null;
             exceptionHandler = null;
             namingPattern = null;
             priority = null;
             daemon = null;
         }
 
         /**
          * Sets the uncaught exception handler for the threads created by the
          * new {@link BasicThreadFactory}.
          *
          * @param exceptionHandler the {@link UncaughtExceptionHandler} (must not be
          * <b>null</b>)
          * @return a reference to this {@link Builder}
          * @throws NullPointerException if the exception handler is <b>null</b>
          */
         public Builder uncaughtExceptionHandler(
                 final Thread.UncaughtExceptionHandler exceptionHandler) {
             this.exceptionHandler = Objects.requireNonNull(exceptionHandler, "handler");
             return this;
         }
 
         /**
          * Sets the {@link ThreadFactory} to be wrapped by the new {@code
          * BasicThreadFactory}.
          *
          * @param factory the wrapped {@link ThreadFactory} (must not be
          * <b>null</b>)
          * @return a reference to this {@link Builder}
          * @throws NullPointerException if the passed in {@link ThreadFactory}
          * is <b>null</b>
          */
         public Builder wrappedFactory(final ThreadFactory factory) {
             this.factory = Objects.requireNonNull(factory, "factory");
             return this;
         }
     }
 
     /** A counter for the threads created by this factory. */
     private final AtomicLong threadCounter;
 
     /** Stores the wrapped factory. */
     private final ThreadFactory wrappedFactory;
 
     /** Stores the uncaught exception handler. */
     private final Thread.UncaughtExceptionHandler uncaughtExceptionHandler;
 
     /** Stores the naming pattern for newly created threads. */
     private final String namingPattern;
 
     /** Stores the priority. */
     private final Integer priority;
 
     /** Stores the daemon status flag. */
     private final Boolean daemon;
 
     /**
      * Creates a new instance of {@link ThreadFactory} and configures it
      * from the specified {@link Builder} object.
      *
      * @param builder the {@link Builder} object
      */
     private BasicThreadFactory(final Builder builder) {
         wrappedFactory = builder.factory != null ? builder.factory : Executors.defaultThreadFactory();
         namingPattern = builder.namingPattern;
         priority = builder.priority;
         daemon = builder.daemon;
         uncaughtExceptionHandler = builder.exceptionHandler;
         threadCounter = new AtomicLong();
     }
 
     /**
      * Gets the daemon flag. This flag determines whether newly created
      * threads should be daemon threads. If <b>true</b>, this factory object
      * calls {@code setDaemon(true)} on the newly created threads. Result can be
      * <b>null</b> if no daemon flag was provided at creation time.
      *
      * @return the daemon flag
      */
     public final Boolean getDaemonFlag() {
         return daemon;
     }
 
     /**
      * Gets the naming pattern for naming newly created threads. Result can
      * be <b>null</b> if no naming pattern was provided.
      *
      * @return the naming pattern
      */
     public final String getNamingPattern() {
         return namingPattern;
     }
 
     /**
      * Gets the priority of the threads created by this factory. Result can
      * be <b>null</b> if no priority was specified.
      *
      * @return the priority for newly created threads
      */
     public final Integer getPriority() {
         return priority;
     }
 
     /**
      * Gets the number of threads this factory has already created. This
      * class maintains an internal counter that is incremented each time the
      * {@link #newThread(Runnable)} method is invoked.
      *
      * @return the number of threads created by this factory
      */
     public long getThreadCount() {
         return threadCounter.get();
     }
 
     /**
      * Gets the {@link UncaughtExceptionHandler} for the threads created by
      * this factory. Result can be <b>null</b> if no handler was provided.
      *
      * @return the {@link UncaughtExceptionHandler}
      */
     public final Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
         return uncaughtExceptionHandler;
     }
 
     /**
      * Gets the wrapped {@link ThreadFactory}. This factory is used for
      * actually creating threads. This method never returns <b>null</b>. If no
      * {@link ThreadFactory} was passed when this object was created, a default
      * thread factory is returned.
      *
      * @return the wrapped {@link ThreadFactory}
      */
     public final ThreadFactory getWrappedFactory() {
         return wrappedFactory;
     }
 
     /**
      * Initializes the specified thread. This method is called by
      * {@link #newThread(Runnable)} after a new thread has been obtained from
      * the wrapped thread factory. It initializes the thread according to the
      * options set for this factory.
      *
      * @param thread the thread to be initialized
      */
     private void initializeThread(final Thread thread) {
         if (getNamingPattern() != null) {
             final Long count = Long.valueOf(threadCounter.incrementAndGet());
             thread.setName(String.format(getNamingPattern(), count));
         }
         if (getUncaughtExceptionHandler() != null) {
             thread.setUncaughtExceptionHandler(getUncaughtExceptionHandler());
         }
         if (getPriority() != null) {
             thread.setPriority(getPriority().intValue());
         }
         if (getDaemonFlag() != null) {
             thread.setDaemon(getDaemonFlag().booleanValue());
         }
     }
 
     /**
      * Creates a new thread. This implementation delegates to the wrapped
      * factory for creating the thread. Then, on the newly created thread the
      * corresponding configuration options are set.
      *
      * @param runnable the {@link Runnable} to be executed by the new thread
      * @return the newly created thread
      */
     @Override
     public Thread newThread(final Runnable runnable) {
         final Thread thread = getWrappedFactory().newThread(runnable);
         initializeThread(thread);
         return thread;
     }
 }