1//===-- llvm/Support/ThreadPool.h - A ThreadPool implementation -*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file defines a crude C++11 based thread pool. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_SUPPORT_THREAD_POOL_H 15#define LLVM_SUPPORT_THREAD_POOL_H 16 17#include "llvm/Support/thread.h" 18 19#include <future> 20 21#include <atomic> 22#include <condition_variable> 23#include <functional> 24#include <memory> 25#include <mutex> 26#include <queue> 27#include <utility> 28 29namespace llvm { 30 31/// A ThreadPool for asynchronous parallel execution on a defined number of 32/// threads. 33/// 34/// The pool keeps a vector of threads alive, waiting on a condition variable 35/// for some work to become available. 36class ThreadPool { 37public: 38 using TaskTy = std::function<void()>; 39 using PackagedTaskTy = std::packaged_task<void()>; 40 41 /// Construct a pool with the number of threads found by 42 /// hardware_concurrency(). 43 ThreadPool(); 44 45 /// Construct a pool of \p ThreadCount threads 46 ThreadPool(unsigned ThreadCount); 47 48 /// Blocking destructor: the pool will wait for all the threads to complete. 49 ~ThreadPool(); 50 51 /// Asynchronous submission of a task to the pool. The returned future can be 52 /// used to wait for the task to finish and is *non-blocking* on destruction. 53 template <typename Function, typename... Args> 54 inline std::shared_future<void> async(Function &&F, Args &&... ArgList) { 55 auto Task = 56 std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...); 57 return asyncImpl(std::move(Task)); 58 } 59 60 /// Asynchronous submission of a task to the pool. The returned future can be 61 /// used to wait for the task to finish and is *non-blocking* on destruction. 62 template <typename Function> 63 inline std::shared_future<void> async(Function &&F) { 64 return asyncImpl(std::forward<Function>(F)); 65 } 66 67 /// Blocking wait for all the threads to complete and the queue to be empty. 68 /// It is an error to try to add new tasks while blocking on this call. 69 void wait(); 70 71private: 72 /// Asynchronous submission of a task to the pool. The returned future can be 73 /// used to wait for the task to finish and is *non-blocking* on destruction. 74 std::shared_future<void> asyncImpl(TaskTy F); 75 76 /// Threads in flight 77 std::vector<llvm::thread> Threads; 78 79 /// Tasks waiting for execution in the pool. 80 std::queue<PackagedTaskTy> Tasks; 81 82 /// Locking and signaling for accessing the Tasks queue. 83 std::mutex QueueLock; 84 std::condition_variable QueueCondition; 85 86 /// Locking and signaling for job completion 87 std::mutex CompletionLock; 88 std::condition_variable CompletionCondition; 89 90 /// Keep track of the number of thread actually busy 91 std::atomic<unsigned> ActiveThreads; 92 93#if LLVM_ENABLE_THREADS // avoids warning for unused variable 94 /// Signal for the destruction of the pool, asking thread to exit. 95 bool EnableFlag; 96#endif 97}; 98} 99 100#endif // LLVM_SUPPORT_THREAD_POOL_H 101