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.
36 using TaskTy = std::function<void()>;
38 /// Construct a pool with the number of core available on the system (or
39 /// whatever the value returned by std::thread::hardware_concurrency() is).
42 /// Construct a pool of \p ThreadCount threads
43 ThreadPool(unsigned ThreadCount);
45 /// Blocking destructor: the pool will wait for all the threads to complete.
48 /// Asynchronous submission of a task to the pool. The returned future can be
49 /// used to wait for the task to finish and is *non-blocking* on destruction.
50 template <typename Function, typename... Args>
51 inline std::shared_future<void> async(Function &&F, Args &&... ArgList) {
53 std::bind(std::forward<Function>(F), std::forward<Args...>(ArgList...));
54 return asyncImpl(Task);
57 /// Asynchronous submission of a task to the pool. The returned future can be
58 /// used to wait for the task to finish and is *non-blocking* on destruction.
59 template <typename Function>
60 inline std::shared_future<void> async(Function &&F) {
64 /// Blocking wait for all the threads to complete and the queue to be empty.
65 /// It is an error to try to add new tasks while blocking on this call.
69 /// Asynchronous submission of a task to the pool. The returned future can be
70 /// used to wait for the task to finish and is *non-blocking* on destruction.
71 std::shared_future<void> asyncImpl(TaskTy f);
74 std::vector<llvm::thread> Threads;
76 /// Tasks waiting for execution in the pool.
77 std::queue<std::packaged_task<void()>> Tasks;
79 /// Locking and signaling for accessing the Tasks queue.
81 std::condition_variable QueueCondition;
83 /// Locking and signaling for job completion
84 std::mutex CompletionLock;
85 std::condition_variable CompletionCondition;
87 /// Keep track of the number of thread actually busy
88 std::atomic<unsigned> ActiveThreads;
90 /// Signal for the destruction of the pool, asking thread to exit.
95 #endif // LLVM_SUPPORT_THREAD_POOL_H