1 //===-- llvm/Support/ThreadPool.h - A ThreadPool implementation -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines a crude C++11 based thread pool. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #ifndef LLVM_SUPPORT_THREADPOOL_H 14 #define LLVM_SUPPORT_THREADPOOL_H 15 16 #include "llvm/Config/llvm-config.h" 17 #include "llvm/Support/Threading.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 using the hardware strategy \p S for mapping hardware 43 /// execution resources (threads, cores, CPUs) 44 /// Defaults to using the maximum execution resources in the system, but 45 /// accounting for the affinity mask. 46 ThreadPool(ThreadPoolStrategy S = hardware_concurrency()); 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> async(Function && F,Args &&...ArgList)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> async(Function && F)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 getThreadCount()71 unsigned getThreadCount() const { return ThreadCount; } 72 73 /// Returns true if the current thread is a worker thread of this thread pool. 74 bool isWorkerThread() const; 75 76 private: workCompletedUnlocked()77 bool workCompletedUnlocked() { return !ActiveThreads && Tasks.empty(); } 78 79 /// Asynchronous submission of a task to the pool. The returned future can be 80 /// used to wait for the task to finish and is *non-blocking* on destruction. 81 std::shared_future<void> asyncImpl(TaskTy F); 82 83 /// Threads in flight 84 std::vector<llvm::thread> Threads; 85 86 /// Tasks waiting for execution in the pool. 87 std::queue<PackagedTaskTy> Tasks; 88 89 /// Locking and signaling for accessing the Tasks queue. 90 std::mutex QueueLock; 91 std::condition_variable QueueCondition; 92 93 /// Signaling for job completion 94 std::condition_variable CompletionCondition; 95 96 /// Keep track of the number of thread actually busy 97 unsigned ActiveThreads = 0; 98 99 #if LLVM_ENABLE_THREADS // avoids warning for unused variable 100 /// Signal for the destruction of the pool, asking thread to exit. 101 bool EnableFlag = true; 102 #endif 103 104 unsigned ThreadCount; 105 }; 106 } 107 108 #endif // LLVM_SUPPORT_THREADPOOL_H 109