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"
20 // concrt.h depends on eh.h for __uncaught_exception declaration
21 // even if we disable exceptions.
25 #include <condition_variable>
35 /// A ThreadPool for asynchronous parallel execution on a defined number of
38 /// The pool keeps a vector of threads alive, waiting on a condition variable
39 /// for some work to become available.
44 using TaskTy = std::function<void()>;
45 using PackagedTaskTy = std::packaged_task<void()>;
47 // MSVC 2013 has a bug and can't use std::packaged_task<void()>;
48 // We force it to use bool(bool) instead.
50 using TaskTy = std::function<bool(bool)>;
51 using PackagedTaskTy = std::packaged_task<bool(bool)>;
54 /// Construct a pool with the number of core available on the system (or
55 /// whatever the value returned by std::thread::hardware_concurrency() is).
58 /// Construct a pool of \p ThreadCount threads
59 ThreadPool(unsigned ThreadCount);
61 /// Blocking destructor: the pool will wait for all the threads to complete.
64 /// Asynchronous submission of a task to the pool. The returned future can be
65 /// used to wait for the task to finish and is *non-blocking* on destruction.
66 template <typename Function, typename... Args>
67 inline std::shared_future<VoidTy> async(Function &&F, Args &&... ArgList) {
69 std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...);
71 return asyncImpl(std::move(Task));
73 // This lambda has to be marked mutable because MSVC 2013's std::bind call
74 // operator isn't const qualified.
75 return asyncImpl([Task](VoidTy) mutable -> VoidTy {
82 /// Asynchronous submission of a task to the pool. The returned future can be
83 /// used to wait for the task to finish and is *non-blocking* on destruction.
84 template <typename Function>
85 inline std::shared_future<VoidTy> async(Function &&F) {
87 return asyncImpl(std::forward<Function>(F));
89 return asyncImpl([F] (VoidTy) -> VoidTy { F(); return VoidTy(); });
93 /// Blocking wait for all the threads to complete and the queue to be empty.
94 /// It is an error to try to add new tasks while blocking on this call.
98 /// Asynchronous submission of a task to the pool. The returned future can be
99 /// used to wait for the task to finish and is *non-blocking* on destruction.
100 std::shared_future<VoidTy> asyncImpl(TaskTy F);
102 /// Threads in flight
103 std::vector<llvm::thread> Threads;
105 /// Tasks waiting for execution in the pool.
106 std::queue<PackagedTaskTy> Tasks;
108 /// Locking and signaling for accessing the Tasks queue.
109 std::mutex QueueLock;
110 std::condition_variable QueueCondition;
112 /// Locking and signaling for job completion
113 std::mutex CompletionLock;
114 std::condition_variable CompletionCondition;
116 /// Keep track of the number of thread actually busy
117 std::atomic<unsigned> ActiveThreads;
119 #if LLVM_ENABLE_THREADS // avoids warning for unused variable
120 /// Signal for the destruction of the pool, asking thread to exit.
126 #endif // LLVM_SUPPORT_THREAD_POOL_H