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#ifndef INCLUDED_SRC_BUILDTOOL_MULTITHREADING_TASK_SYSTEM_HPP
#define INCLUDED_SRC_BUILDTOOL_MULTITHREADING_TASK_SYSTEM_HPP
#include <algorithm>
#include <atomic>
#include <thread>
#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_;
}
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};
WaitableOneWayFlag queues_read_{};
WaitableZeroCounter num_threads_running_{};
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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