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/Config/llvm-config.h" 18 #include "llvm/Support/thread.h" 19 20 #include <future> 21 22 #include <atomic> 23 #include <condition_variable> 24 #include <functional> 25 #include <memory> 26 #include <mutex> 27 #include <queue> 28 #include <utility> 29 30 namespace llvm { 31 32 /// A ThreadPool for asynchronous parallel execution on a defined number of 33 /// threads. 34 /// 35 /// The pool keeps a vector of threads alive, waiting on a condition variable 36 /// for some work to become available. 37 class ThreadPool { 38 public: 39 using TaskTy = std::function<void()>; 40 using PackagedTaskTy = std::packaged_task<void()>; 41 42 /// Construct a pool with the number of threads found by 43 /// hardware_concurrency(). 44 ThreadPool(); 45 46 /// Construct a pool of \p ThreadCount threads 47 ThreadPool(unsigned ThreadCount); 48 49 /// Blocking destructor: the pool will wait for all the threads to complete. 50 ~ThreadPool(); 51 52 /// Asynchronous submission of a task to the pool. The returned future can be 53 /// used to wait for the task to finish and is *non-blocking* on destruction. 54 template <typename Function, typename... Args> async(Function && F,Args &&...ArgList)55 inline std::shared_future<void> async(Function &&F, Args &&... ArgList) { 56 auto Task = 57 std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...); 58 return asyncImpl(std::move(Task)); 59 } 60 61 /// Asynchronous submission of a task to the pool. The returned future can be 62 /// used to wait for the task to finish and is *non-blocking* on destruction. 63 template <typename Function> async(Function && F)64 inline std::shared_future<void> async(Function &&F) { 65 return asyncImpl(std::forward<Function>(F)); 66 } 67 68 /// Blocking wait for all the threads to complete and the queue to be empty. 69 /// It is an error to try to add new tasks while blocking on this call. 70 void wait(); 71 72 private: 73 /// Asynchronous submission of a task to the pool. The returned future can be 74 /// used to wait for the task to finish and is *non-blocking* on destruction. 75 std::shared_future<void> asyncImpl(TaskTy F); 76 77 /// Threads in flight 78 std::vector<llvm::thread> Threads; 79 80 /// Tasks waiting for execution in the pool. 81 std::queue<PackagedTaskTy> Tasks; 82 83 /// Locking and signaling for accessing the Tasks queue. 84 std::mutex QueueLock; 85 std::condition_variable QueueCondition; 86 87 /// Locking and signaling for job completion 88 std::mutex CompletionLock; 89 std::condition_variable CompletionCondition; 90 91 /// Keep track of the number of thread actually busy 92 std::atomic<unsigned> ActiveThreads; 93 94 #if LLVM_ENABLE_THREADS // avoids warning for unused variable 95 /// Signal for the destruction of the pool, asking thread to exit. 96 bool EnableFlag; 97 #endif 98 }; 99 } 100 101 #endif // LLVM_SUPPORT_THREAD_POOL_H 102