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) 033public final class Callables { 034 private Callables() {} 035 036 /** Creates a {@code Callable} which immediately returns a preset value each time it is called. */ 037 public static <T> Callable<T> returning(final @Nullable T value) { 038 return new Callable<T>() { 039 @Override 040 public T call() { 041 return value; 042 } 043 }; 044 } 045 046 /** 047 * Creates an {@link AsyncCallable} from a {@link Callable}. 048 * 049 * <p>The {@link AsyncCallable} returns the {@link ListenableFuture} resulting from {@link 050 * ListeningExecutorService#submit(Callable)}. 051 * 052 * @since 20.0 053 */ 054 @Beta 055 @GwtIncompatible 056 public static <T> AsyncCallable<T> asAsyncCallable( 057 final Callable<T> callable, final ListeningExecutorService listeningExecutorService) { 058 checkNotNull(callable); 059 checkNotNull(listeningExecutorService); 060 return new AsyncCallable<T>() { 061 @Override 062 public ListenableFuture<T> call() throws Exception { 063 return listeningExecutorService.submit(callable); 064 } 065 }; 066 } 067 068 /** 069 * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is 070 * running will have the given name. 071 * 072 * 073 * @param callable The callable to wrap 074 * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once 075 * for each invocation of the wrapped callable. 076 */ 077 @GwtIncompatible // threads 078 static <T> Callable<T> threadRenaming( 079 final Callable<T> callable, final Supplier<String> nameSupplier) { 080 checkNotNull(nameSupplier); 081 checkNotNull(callable); 082 return new Callable<T>() { 083 @Override 084 public T call() throws Exception { 085 Thread currentThread = Thread.currentThread(); 086 String oldName = currentThread.getName(); 087 boolean restoreName = trySetName(nameSupplier.get(), currentThread); 088 try { 089 return callable.call(); 090 } finally { 091 if (restoreName) { 092 boolean unused = trySetName(oldName, currentThread); 093 } 094 } 095 } 096 }; 097 } 098 099 /** 100 * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is 101 * running with have the given name. 102 * 103 * 104 * @param task The Runnable to wrap 105 * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once 106 * for each invocation of the wrapped callable. 107 */ 108 @GwtIncompatible // threads 109 static Runnable threadRenaming(final Runnable task, final Supplier<String> nameSupplier) { 110 checkNotNull(nameSupplier); 111 checkNotNull(task); 112 return new Runnable() { 113 @Override 114 public void run() { 115 Thread currentThread = Thread.currentThread(); 116 String oldName = currentThread.getName(); 117 boolean restoreName = trySetName(nameSupplier.get(), currentThread); 118 try { 119 task.run(); 120 } finally { 121 if (restoreName) { 122 boolean unused = trySetName(oldName, currentThread); 123 } 124 } 125 } 126 }; 127 } 128 129 /** Tries to set name of the given {@link Thread}, returns true if successful. */ 130 @GwtIncompatible // threads 131 private static boolean trySetName(final String threadName, Thread currentThread) { 132 // In AppEngine, this will always fail. Should we test for that explicitly using 133 // MoreExecutors.isAppEngine? More generally, is there a way to see if we have the modifyThread 134 // permission without catching an exception? 135 try { 136 currentThread.setName(threadName); 137 return true; 138 } catch (SecurityException e) { 139 return false; 140 } 141 } 142}