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_THREAD_POOL_H 14 #define LLVM_SUPPORT_THREAD_POOL_H 15 16 #include "llvm/Config/llvm-config.h" 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 29 namespace 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. 36 class ThreadPool { 37 public: 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 71 private: 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