1/*
2 * Copyright (C) 2009 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.util.concurrent;
18
19import static com.google.common.base.Preconditions.checkNotNull;
20
21import com.google.common.base.Supplier;
22
23import java.util.concurrent.Callable;
24
25import javax.annotation.Nullable;
26
27/**
28 * Static utility methods pertaining to the {@link Callable} interface.
29 *
30 * @author Isaac Shum
31 * @since 1.0
32 */
33public final class Callables {
34  private Callables() {}
35
36  /**
37   * Creates a {@code Callable} which immediately returns a preset value each
38   * time it is called.
39   */
40  public static <T> Callable<T> returning(final @Nullable T value) {
41    return new Callable<T>() {
42      @Override public T call() {
43        return value;
44      }
45    };
46  }
47
48  /**
49   * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
50   * running will have the given name.
51   *
52   *
53   * @param callable The callable to wrap
54   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
55   *     for each invocation of the wrapped callable.
56   */
57  static <T> Callable<T> threadRenaming(final Callable<T> callable,
58      final Supplier<String> nameSupplier) {
59    checkNotNull(nameSupplier);
60    checkNotNull(callable);
61    return new Callable<T>() {
62      @Override public T call() throws Exception {
63        Thread currentThread = Thread.currentThread();
64        String oldName = currentThread.getName();
65        boolean restoreName = trySetName(nameSupplier.get(), currentThread);
66        try {
67          return callable.call();
68        } finally {
69          if (restoreName) {
70            trySetName(oldName, currentThread);
71          }
72        }
73      }
74    };
75  }
76
77  /**
78   * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
79   * running with have the given name.
80   *
81   *
82   * @param task The Runnable to wrap
83   * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
84   *     for each invocation of the wrapped callable.
85   */
86  static Runnable threadRenaming(final Runnable task, final Supplier<String> nameSupplier) {
87    checkNotNull(nameSupplier);
88    checkNotNull(task);
89    return new Runnable() {
90      @Override public void run() {
91        Thread currentThread = Thread.currentThread();
92        String oldName = currentThread.getName();
93        boolean restoreName = trySetName(nameSupplier.get(), currentThread);
94        try {
95          task.run();
96        } finally {
97          if (restoreName) {
98            trySetName(oldName, currentThread);
99          }
100        }
101      }
102    };
103  }
104
105  /** Tries to set name of the given {@link Thread}, returns true if successful. */
106  private static boolean trySetName(final String threadName, Thread currentThread) {
107    // In AppEngine this will always fail, should we test for that explicitly using
108    // MoreExecutors.isAppEngine.  More generally, is there a way to see if we have the modifyThread
109    // permission without catching an exception?
110    try {
111      currentThread.setName(threadName);
112      return true;
113    } catch (SecurityException e) {
114      return false;
115    }
116  }
117}
118