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// Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef INCLUDED_SRC_BUILDTOOL_MULTITHREADING_TASK_SYSTEM_HPP
#define INCLUDED_SRC_BUILDTOOL_MULTITHREADING_TASK_SYSTEM_HPP
#include <algorithm>
#include <atomic>
#include <cstddef>
#include <thread>
#include <utility> // std::forward
#include <vector>
#include "src/buildtool/multithreading/notification_queue.hpp"
class TaskSystem {
public:
// Constructors create as many threads as specified (or
// std::thread::hardware_concurrency() many if not specified) running
// `TaskSystem::Run(index)` on them, where `index` is their position in
// `threads_`
TaskSystem();
explicit TaskSystem(std::size_t number_of_threads);
TaskSystem(TaskSystem const&) = delete;
TaskSystem(TaskSystem&&) = delete;
auto operator=(TaskSystem const&) -> TaskSystem& = delete;
auto operator=(TaskSystem&&) -> TaskSystem& = delete;
// Destructor calls sets to "done" all notification queues and joins the
// threads. Note that joining the threads will wait until the Run method
// they are running is finished
~TaskSystem();
// Queue a task. Task will be added to the first notification queue that is
// found to be unlocked or, if none is found (after kNumberOfAttemps
// iterations), to the one in `index+1` position waiting until it's
// unlocked.
template <typename FunctionType>
void QueueTask(FunctionType&& f) noexcept {
auto idx = index_++;
for (std::size_t i = 0; i < thread_count_ * kNumberOfAttempts; ++i) {
if (queues_[(idx + i) % thread_count_].try_push(
std::forward<FunctionType>(f))) {
return;
}
}
queues_[idx % thread_count_].push(std::forward<FunctionType>(f));
}
[[nodiscard]] auto NumberOfThreads() const noexcept -> std::size_t {
return thread_count_;
}
// Initiate shutdown, skip execution of pending tasks
void Shutdown() noexcept;
// Wait for all queues to become empty _and_ all tasks to finish.
void Finish() noexcept;
private:
std::size_t const thread_count_{
std::max(1U, std::thread::hardware_concurrency())};
std::vector<std::thread> threads_;
std::vector<NotificationQueue> queues_;
std::atomic<std::size_t> index_{0};
std::atomic<bool> shutdown_;
WaitableZeroCounter total_workload_;
static constexpr std::size_t kNumberOfAttempts = 5;
void Run(std::size_t idx);
};
#endif // INCLUDED_SRC_BUILDTOOL_MULTITHREADING_TASK_SYSTEM_HPP
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