001/*
002 * Copyright (C) 2009 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.checkNotNull;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.common.annotations.GwtIncompatible;
021import com.google.common.annotations.J2ktIncompatible;
022import com.google.common.base.Supplier;
023import java.util.concurrent.Callable;
024import org.checkerframework.checker.nullness.qual.Nullable;
025
026/**
027 * Static utility methods pertaining to the {@link Callable} interface.
028 *
029 * @author Isaac Shum
030 * @since 1.0
031 */
032@GwtCompatible(emulated = true)
033@ElementTypesAreNonnullByDefault
034public final class Callables {
035  private Callables() {}
036
037  /** Creates a {@code Callable} which immediately returns a preset value each time it is called. */
038  public static <T extends @Nullable Object> Callable<T> returning(@ParametricNullness T value) {
039    return () -> value;
040  }
041
042  /**
043   * Creates an {@link AsyncCallable} from a {@link Callable}.
044   *
045   * <p>The {@link AsyncCallable} returns the {@link ListenableFuture} resulting from {@link
046   * ListeningExecutorService#submit(Callable)}.
047   *
048   * @since 20.0
049   */
050  @J2ktIncompatible
051  @GwtIncompatible
052  public static <T extends @Nullable Object> AsyncCallable<T> asAsyncCallable(
053      Callable<T> callable, ListeningExecutorService listeningExecutorService) {
054    checkNotNull(callable);
055    checkNotNull(listeningExecutorService);
056    return () -> listeningExecutorService.submit(callable);
057  }
058
059  /**
060   * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
061   * running will have the given name.
062   *
063   * @param callable The callable to wrap
064   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
065   *     for each invocation of the wrapped callable.
066   */
067  @J2ktIncompatible
068  @GwtIncompatible // threads
069  static <T extends @Nullable Object> Callable<T> threadRenaming(
070      Callable<T> callable, Supplier<String> nameSupplier) {
071    checkNotNull(nameSupplier);
072    checkNotNull(callable);
073    return () -> {
074      Thread currentThread = Thread.currentThread();
075      String oldName = currentThread.getName();
076      boolean restoreName = trySetName(nameSupplier.get(), currentThread);
077      try {
078        return callable.call();
079      } finally {
080        if (restoreName) {
081          boolean unused = trySetName(oldName, currentThread);
082        }
083      }
084    };
085  }
086
087  /**
088   * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
089   * running with have the given name.
090   *
091   * @param task The Runnable to wrap
092   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
093   *     for each invocation of the wrapped callable.
094   */
095  @J2ktIncompatible
096  @GwtIncompatible // threads
097  static Runnable threadRenaming(Runnable task, Supplier<String> nameSupplier) {
098    checkNotNull(nameSupplier);
099    checkNotNull(task);
100    return () -> {
101      Thread currentThread = Thread.currentThread();
102      String oldName = currentThread.getName();
103      boolean restoreName = trySetName(nameSupplier.get(), currentThread);
104      try {
105        task.run();
106      } finally {
107        if (restoreName) {
108          boolean unused = trySetName(oldName, currentThread);
109        }
110      }
111    };
112  }
113
114  /** Tries to set name of the given {@link Thread}, returns true if successful. */
115  @J2ktIncompatible
116  @GwtIncompatible // threads
117  private static boolean trySetName(String threadName, Thread currentThread) {
118    /*
119     * setName should usually succeed, but the security manager can prohibit it. Is there a way to
120     * see if we have the modifyThread permission without catching an exception?
121     */
122    try {
123      currentThread.setName(threadName);
124      return true;
125    } catch (SecurityException e) {
126      return false;
127    }
128  }
129}