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.
24 // Disable warnings from ppltasks.h transitively included by <future>.
26 #pragma warning(disable:4530)
27 #pragma warning(disable:4062)
36 #include <condition_variable>
45 /// A ThreadPool for asynchronous parallel execution on a defined number of
48 /// The pool keeps a vector of threads alive, waiting on a condition variable
49 /// for some work to become available.
54 using TaskTy = std::function<void()>;
55 using PackagedTaskTy = std::packaged_task<void()>;
57 // MSVC 2013 has a bug and can't use std::packaged_task<void()>;
58 // We force it to use bool(bool) instead.
60 using TaskTy = std::function<bool(bool)>;
61 using PackagedTaskTy = std::packaged_task<bool(bool)>;
64 /// Construct a pool with the number of core available on the system (or
65 /// whatever the value returned by std::thread::hardware_concurrency() is).
68 /// Construct a pool of \p ThreadCount threads
69 ThreadPool(unsigned ThreadCount);
71 /// Blocking destructor: the pool will wait for all the threads to complete.
74 /// Asynchronous submission of a task to the pool. The returned future can be
75 /// used to wait for the task to finish and is *non-blocking* on destruction.
76 template <typename Function, typename... Args>
77 inline std::shared_future<VoidTy> async(Function &&F, Args &&... ArgList) {
79 std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...);
81 return asyncImpl(std::move(Task));
83 // This lambda has to be marked mutable because MSVC 2013's std::bind call
84 // operator isn't const qualified.
85 return asyncImpl([Task](VoidTy) mutable -> VoidTy {
92 /// Asynchronous submission of a task to the pool. The returned future can be
93 /// used to wait for the task to finish and is *non-blocking* on destruction.
94 template <typename Function>
95 inline std::shared_future<VoidTy> async(Function &&F) {
97 return asyncImpl(std::forward<Function>(F));
99 return asyncImpl([F] (VoidTy) -> VoidTy { F(); return VoidTy(); });
103 /// Blocking wait for all the threads to complete and the queue to be empty.
104 /// It is an error to try to add new tasks while blocking on this call.
108 /// Asynchronous submission of a task to the pool. The returned future can be
109 /// used to wait for the task to finish and is *non-blocking* on destruction.
110 std::shared_future<VoidTy> asyncImpl(TaskTy F);
112 /// Threads in flight
113 std::vector<llvm::thread> Threads;
115 /// Tasks waiting for execution in the pool.
116 std::queue<PackagedTaskTy> Tasks;
118 /// Locking and signaling for accessing the Tasks queue.
119 std::mutex QueueLock;
120 std::condition_variable QueueCondition;
122 /// Locking and signaling for job completion
123 std::mutex CompletionLock;
124 std::condition_variable CompletionCondition;
126 /// Keep track of the number of thread actually busy
127 std::atomic<unsigned> ActiveThreads;
129 #if LLVM_ENABLE_THREADS // avoids warning for unused variable
130 /// Signal for the destruction of the pool, asking thread to exit.
136 #endif // LLVM_SUPPORT_THREAD_POOL_H