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.Beta;
020import com.google.common.annotations.GwtCompatible;
021import com.google.common.annotations.GwtIncompatible;
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  @Beta
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  @GwtIncompatible // threads
068  static <T extends @Nullable Object> Callable<T> threadRenaming(
069      Callable<T> callable, Supplier<String> nameSupplier) {
070    checkNotNull(nameSupplier);
071    checkNotNull(callable);
072    return () -> {
073      Thread currentThread = Thread.currentThread();
074      String oldName = currentThread.getName();
075      boolean restoreName = trySetName(nameSupplier.get(), currentThread);
076      try {
077        return callable.call();
078      } finally {
079        if (restoreName) {
080          boolean unused = trySetName(oldName, currentThread);
081        }
082      }
083    };
084  }
085
086  /**
087   * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
088   * running with have the given name.
089   *
090   * @param task The Runnable to wrap
091   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
092   *     for each invocation of the wrapped callable.
093   */
094  @GwtIncompatible // threads
095  static Runnable threadRenaming(Runnable task, Supplier<String> nameSupplier) {
096    checkNotNull(nameSupplier);
097    checkNotNull(task);
098    return () -> {
099      Thread currentThread = Thread.currentThread();
100      String oldName = currentThread.getName();
101      boolean restoreName = trySetName(nameSupplier.get(), currentThread);
102      try {
103        task.run();
104      } finally {
105        if (restoreName) {
106          boolean unused = trySetName(oldName, currentThread);
107        }
108      }
109    };
110  }
111
112  /** Tries to set name of the given {@link Thread}, returns true if successful. */
113  @GwtIncompatible // threads
114  private static boolean trySetName(String threadName, Thread currentThread) {
115    /*
116     * setName should usually succeed, but the security manager can prohibit it. Is there a way to
117     * see if we have the modifyThread permission without catching an exception?
118     */
119    try {
120      currentThread.setName(threadName);
121      return true;
122    } catch (SecurityException e) {
123      return false;
124    }
125  }
126}