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(
039      @ParametricNullness final T value) {
040    return new Callable<T>() {
041      @Override
042      @ParametricNullness
043      public T call() {
044        return value;
045      }
046    };
047  }
048
049  /**
050   * Creates an {@link AsyncCallable} from a {@link Callable}.
051   *
052   * <p>The {@link AsyncCallable} returns the {@link ListenableFuture} resulting from {@link
053   * ListeningExecutorService#submit(Callable)}.
054   *
055   * @since 20.0
056   */
057  @Beta
058  @GwtIncompatible
059  public static <T extends @Nullable Object> AsyncCallable<T> asAsyncCallable(
060      final Callable<T> callable, final ListeningExecutorService listeningExecutorService) {
061    checkNotNull(callable);
062    checkNotNull(listeningExecutorService);
063    return new AsyncCallable<T>() {
064      @Override
065      public ListenableFuture<T> call() throws Exception {
066        return listeningExecutorService.submit(callable);
067      }
068    };
069  }
070
071  /**
072   * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
073   * running will have the given name.
074   *
075   * @param callable The callable to wrap
076   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
077   *     for each invocation of the wrapped callable.
078   */
079  @GwtIncompatible // threads
080  static <T extends @Nullable Object> Callable<T> threadRenaming(
081      final Callable<T> callable, final Supplier<String> nameSupplier) {
082    checkNotNull(nameSupplier);
083    checkNotNull(callable);
084    return new Callable<T>() {
085      @Override
086      @ParametricNullness
087      public T call() throws Exception {
088        Thread currentThread = Thread.currentThread();
089        String oldName = currentThread.getName();
090        boolean restoreName = trySetName(nameSupplier.get(), currentThread);
091        try {
092          return callable.call();
093        } finally {
094          if (restoreName) {
095            boolean unused = trySetName(oldName, currentThread);
096          }
097        }
098      }
099    };
100  }
101
102  /**
103   * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
104   * running with have the given name.
105   *
106   * @param task The Runnable to wrap
107   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
108   *     for each invocation of the wrapped callable.
109   */
110  @GwtIncompatible // threads
111  static Runnable threadRenaming(final Runnable task, final Supplier<String> nameSupplier) {
112    checkNotNull(nameSupplier);
113    checkNotNull(task);
114    return new Runnable() {
115      @Override
116      public void run() {
117        Thread currentThread = Thread.currentThread();
118        String oldName = currentThread.getName();
119        boolean restoreName = trySetName(nameSupplier.get(), currentThread);
120        try {
121          task.run();
122        } finally {
123          if (restoreName) {
124            boolean unused = trySetName(oldName, currentThread);
125          }
126        }
127      }
128    };
129  }
130
131  /** Tries to set name of the given {@link Thread}, returns true if successful. */
132  @GwtIncompatible // threads
133  private static boolean trySetName(final String threadName, Thread currentThread) {
134    /*
135     * setName should usually succeed, but the security manager can prohibit it. Is there a way to
136     * see if we have the modifyThread permission without catching an exception?
137     */
138    try {
139      currentThread.setName(threadName);
140      return true;
141    } catch (SecurityException e) {
142      return false;
143    }
144  }
145}