1 //===-- llvm/Support/ThreadPool.h - A ThreadPool implementation -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines a crude C++11 based thread pool.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_SUPPORT_THREAD_POOL_H
15 #define LLVM_SUPPORT_THREAD_POOL_H
17 #include "llvm/Support/thread.h"
19 #include <condition_variable>
29 /// A ThreadPool for asynchronous parallel execution on a defined number of
32 /// The pool keeps a vector of threads alive, waiting on a condition variable
33 /// for some work to become available.
38 using TaskTy = std::function<void()>;
39 using PackagedTaskTy = std::packaged_task<void()>;
41 // MSVC 2013 has a bug and can't use std::packaged_task<void()>;
42 // We force it to use bool(bool) instead.
44 using TaskTy = std::function<bool(bool)>;
45 using PackagedTaskTy = std::packaged_task<bool(bool)>;
48 /// Construct a pool with the number of core available on the system (or
49 /// whatever the value returned by std::thread::hardware_concurrency() is).
52 /// Construct a pool of \p ThreadCount threads
53 ThreadPool(unsigned ThreadCount);
55 /// Blocking destructor: the pool will wait for all the threads to complete.
58 /// Asynchronous submission of a task to the pool. The returned future can be
59 /// used to wait for the task to finish and is *non-blocking* on destruction.
60 template <typename Function, typename... Args>
61 inline std::shared_future<VoidTy> async(Function &&F, Args &&... ArgList) {
63 std::bind(std::forward<Function>(F), std::forward<Args...>(ArgList...));
65 return asyncImpl(std::move(Task));
67 return asyncImpl([Task] (VoidTy) -> VoidTy { Task(); return VoidTy(); });
71 /// Asynchronous submission of a task to the pool. The returned future can be
72 /// used to wait for the task to finish and is *non-blocking* on destruction.
73 template <typename Function>
74 inline std::shared_future<VoidTy> async(Function &&F) {
76 return asyncImpl(std::forward<Function>(F));
78 return asyncImpl([F] (VoidTy) -> VoidTy { F(); return VoidTy(); });
82 /// Blocking wait for all the threads to complete and the queue to be empty.
83 /// It is an error to try to add new tasks while blocking on this call.
87 /// Asynchronous submission of a task to the pool. The returned future can be
88 /// used to wait for the task to finish and is *non-blocking* on destruction.
89 std::shared_future<VoidTy> asyncImpl(TaskTy F);
92 std::vector<llvm::thread> Threads;
94 /// Tasks waiting for execution in the pool.
95 std::queue<PackagedTaskTy> Tasks;
97 /// Locking and signaling for accessing the Tasks queue.
99 std::condition_variable QueueCondition;
101 /// Locking and signaling for job completion
102 std::mutex CompletionLock;
103 std::condition_variable CompletionCondition;
105 /// Keep track of the number of thread actually busy
106 std::atomic<unsigned> ActiveThreads;
108 #if LLVM_ENABLE_THREADS // avoids warning for unused variable
109 /// Signal for the destruction of the pool, asking thread to exit.
115 #endif // LLVM_SUPPORT_THREAD_POOL_H