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