| //===-- llvm/Support/ThreadPool.h - A ThreadPool implementation -*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines a crude C++11 based thread pool. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_SUPPORT_THREAD_POOL_H |
| #define LLVM_SUPPORT_THREAD_POOL_H |
| |
| #include "llvm/Config/llvm-config.h" |
| #include "llvm/Support/Threading.h" |
| #include "llvm/Support/thread.h" |
| |
| #include <future> |
| |
| #include <atomic> |
| #include <condition_variable> |
| #include <functional> |
| #include <memory> |
| #include <mutex> |
| #include <queue> |
| #include <utility> |
| |
| namespace llvm { |
| |
| /// A ThreadPool for asynchronous parallel execution on a defined number of |
| /// threads. |
| /// |
| /// The pool keeps a vector of threads alive, waiting on a condition variable |
| /// for some work to become available. |
| class ThreadPool { |
| public: |
| using TaskTy = std::function<void()>; |
| using PackagedTaskTy = std::packaged_task<void()>; |
| |
| /// Construct a pool using the hardware strategy \p S for mapping hardware |
| /// execution resources (threads, cores, CPUs) |
| /// Defaults to using the maximum execution resources in the system, but |
| /// accounting for the affinity mask. |
| ThreadPool(ThreadPoolStrategy S = hardware_concurrency()); |
| |
| /// Blocking destructor: the pool will wait for all the threads to complete. |
| ~ThreadPool(); |
| |
| /// Asynchronous submission of a task to the pool. The returned future can be |
| /// used to wait for the task to finish and is *non-blocking* on destruction. |
| template <typename Function, typename... Args> |
| inline std::shared_future<void> async(Function &&F, Args &&... ArgList) { |
| auto Task = |
| std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...); |
| return asyncImpl(std::move(Task)); |
| } |
| |
| /// Asynchronous submission of a task to the pool. The returned future can be |
| /// used to wait for the task to finish and is *non-blocking* on destruction. |
| template <typename Function> |
| inline std::shared_future<void> async(Function &&F) { |
| return asyncImpl(std::forward<Function>(F)); |
| } |
| |
| /// Blocking wait for all the threads to complete and the queue to be empty. |
| /// It is an error to try to add new tasks while blocking on this call. |
| void wait(); |
| |
| unsigned getThreadCount() const { return ThreadCount; } |
| |
| private: |
| bool workCompletedUnlocked() { return !ActiveThreads && Tasks.empty(); } |
| |
| /// Asynchronous submission of a task to the pool. The returned future can be |
| /// used to wait for the task to finish and is *non-blocking* on destruction. |
| std::shared_future<void> asyncImpl(TaskTy F); |
| |
| /// Threads in flight |
| std::vector<llvm::thread> Threads; |
| |
| /// Tasks waiting for execution in the pool. |
| std::queue<PackagedTaskTy> Tasks; |
| |
| /// Locking and signaling for accessing the Tasks queue. |
| std::mutex QueueLock; |
| std::condition_variable QueueCondition; |
| |
| /// Signaling for job completion |
| std::condition_variable CompletionCondition; |
| |
| /// Keep track of the number of thread actually busy |
| unsigned ActiveThreads = 0; |
| |
| #if LLVM_ENABLE_THREADS // avoids warning for unused variable |
| /// Signal for the destruction of the pool, asking thread to exit. |
| bool EnableFlag = true; |
| #endif |
| |
| unsigned ThreadCount; |
| }; |
| } |
| |
| #endif // LLVM_SUPPORT_THREAD_POOL_H |