001/*
002 * Copyright (C) 2010 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.util.concurrent;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019import static java.util.Objects.requireNonNull;
020
021import com.google.common.annotations.GwtIncompatible;
022import com.google.common.annotations.J2ktIncompatible;
023import com.google.errorprone.annotations.CanIgnoreReturnValue;
024import java.lang.Thread.UncaughtExceptionHandler;
025import java.util.Locale;
026import java.util.concurrent.Executors;
027import java.util.concurrent.ThreadFactory;
028import java.util.concurrent.atomic.AtomicLong;
029import javax.annotation.CheckForNull;
030
031/**
032 * A ThreadFactory builder, providing any combination of these features:
033 *
034 * <ul>
035 *   <li>whether threads should be marked as {@linkplain Thread#setDaemon daemon} threads
036 *   <li>a {@linkplain ThreadFactoryBuilder#setNameFormat naming format}
037 *   <li>a {@linkplain Thread#setPriority thread priority}
038 *   <li>an {@linkplain Thread#setUncaughtExceptionHandler uncaught exception handler}
039 *   <li>a {@linkplain ThreadFactory#newThread backing thread factory}
040 * </ul>
041 *
042 * <p>If no backing thread factory is provided, a default backing thread factory is used as if by
043 * calling {@code setThreadFactory(}{@link Executors#defaultThreadFactory()}{@code )}.
044 *
045 * @author Kurt Alfred Kluever
046 * @since 4.0
047 */
048@J2ktIncompatible
049@GwtIncompatible
050@ElementTypesAreNonnullByDefault
051public final class ThreadFactoryBuilder {
052  @CheckForNull private String nameFormat = null;
053  @CheckForNull private Boolean daemon = null;
054  @CheckForNull private Integer priority = null;
055  @CheckForNull private UncaughtExceptionHandler uncaughtExceptionHandler = null;
056  @CheckForNull private ThreadFactory backingThreadFactory = null;
057
058  /** Creates a new {@link ThreadFactory} builder. */
059  public ThreadFactoryBuilder() {}
060
061  /**
062   * Sets the naming format to use when naming threads ({@link Thread#setName}) which are created
063   * with this ThreadFactory.
064   *
065   * @param nameFormat a {@link String#format(String, Object...)}-compatible format String, to which
066   *     a unique integer (0, 1, etc.) will be supplied as the single parameter. This integer will
067   *     be unique to the built instance of the ThreadFactory and will be assigned sequentially. For
068   *     example, {@code "rpc-pool-%d"} will generate thread names like {@code "rpc-pool-0"}, {@code
069   *     "rpc-pool-1"}, {@code "rpc-pool-2"}, etc.
070   * @return this for the builder pattern
071   */
072  @CanIgnoreReturnValue
073  public ThreadFactoryBuilder setNameFormat(String nameFormat) {
074    String unused = format(nameFormat, 0); // fail fast if the format is bad or null
075    this.nameFormat = nameFormat;
076    return this;
077  }
078
079  /**
080   * Sets daemon or not for new threads created with this ThreadFactory.
081   *
082   * @param daemon whether or not new Threads created with this ThreadFactory will be daemon threads
083   * @return this for the builder pattern
084   */
085  @CanIgnoreReturnValue
086  public ThreadFactoryBuilder setDaemon(boolean daemon) {
087    this.daemon = daemon;
088    return this;
089  }
090
091  /**
092   * Sets the priority for new threads created with this ThreadFactory.
093   *
094   * <p><b>Warning:</b> relying on the thread scheduler is <a
095   * href="http://errorprone.info/bugpattern/ThreadPriorityCheck">discouraged</a>.
096   *
097   * @param priority the priority for new Threads created with this ThreadFactory
098   * @return this for the builder pattern
099   */
100  @CanIgnoreReturnValue
101  public ThreadFactoryBuilder setPriority(int priority) {
102    // Thread#setPriority() already checks for validity. These error messages
103    // are nicer though and will fail-fast.
104    checkArgument(
105        priority >= Thread.MIN_PRIORITY,
106        "Thread priority (%s) must be >= %s",
107        priority,
108        Thread.MIN_PRIORITY);
109    checkArgument(
110        priority <= Thread.MAX_PRIORITY,
111        "Thread priority (%s) must be <= %s",
112        priority,
113        Thread.MAX_PRIORITY);
114    this.priority = priority;
115    return this;
116  }
117
118  /**
119   * Sets the {@link UncaughtExceptionHandler} for new threads created with this ThreadFactory.
120   *
121   * @param uncaughtExceptionHandler the uncaught exception handler for new Threads created with
122   *     this ThreadFactory
123   * @return this for the builder pattern
124   */
125  @CanIgnoreReturnValue
126  public ThreadFactoryBuilder setUncaughtExceptionHandler(
127      UncaughtExceptionHandler uncaughtExceptionHandler) {
128    this.uncaughtExceptionHandler = checkNotNull(uncaughtExceptionHandler);
129    return this;
130  }
131
132  /**
133   * Sets the backing {@link ThreadFactory} for new threads created with this ThreadFactory. Threads
134   * will be created by invoking #newThread(Runnable) on this backing {@link ThreadFactory}.
135   *
136   * @param backingThreadFactory the backing {@link ThreadFactory} which will be delegated to during
137   *     thread creation.
138   * @return this for the builder pattern
139   * @see MoreExecutors
140   */
141  @CanIgnoreReturnValue
142  public ThreadFactoryBuilder setThreadFactory(ThreadFactory backingThreadFactory) {
143    this.backingThreadFactory = checkNotNull(backingThreadFactory);
144    return this;
145  }
146
147  /**
148   * Returns a new thread factory using the options supplied during the building process. After
149   * building, it is still possible to change the options used to build the ThreadFactory and/or
150   * build again. State is not shared amongst built instances.
151   *
152   * @return the fully constructed {@link ThreadFactory}
153   */
154  public ThreadFactory build() {
155    return doBuild(this);
156  }
157
158  // Split out so that the anonymous ThreadFactory can't contain a reference back to the builder.
159  // At least, I assume that's why. TODO(cpovirk): Check, and maybe add a test for this.
160  private static ThreadFactory doBuild(ThreadFactoryBuilder builder) {
161    String nameFormat = builder.nameFormat;
162    Boolean daemon = builder.daemon;
163    Integer priority = builder.priority;
164    UncaughtExceptionHandler uncaughtExceptionHandler = builder.uncaughtExceptionHandler;
165    ThreadFactory backingThreadFactory =
166        (builder.backingThreadFactory != null)
167            ? builder.backingThreadFactory
168            : Executors.defaultThreadFactory();
169    AtomicLong count = (nameFormat != null) ? new AtomicLong(0) : null;
170    return new ThreadFactory() {
171      @Override
172      public Thread newThread(Runnable runnable) {
173        Thread thread = backingThreadFactory.newThread(runnable);
174        // TODO(b/139735208): Figure out what to do when the factory returns null.
175        requireNonNull(thread);
176        if (nameFormat != null) {
177          // requireNonNull is safe because we create `count` if (and only if) we have a nameFormat.
178          thread.setName(format(nameFormat, requireNonNull(count).getAndIncrement()));
179        }
180        if (daemon != null) {
181          thread.setDaemon(daemon);
182        }
183        if (priority != null) {
184          thread.setPriority(priority);
185        }
186        if (uncaughtExceptionHandler != null) {
187          thread.setUncaughtExceptionHandler(uncaughtExceptionHandler);
188        }
189        return thread;
190      }
191    };
192  }
193
194  private static String format(String format, Object... args) {
195    return String.format(Locale.ROOT, format, args);
196  }
197}