ecs/include/ecs/core/utils/thread_pool/pool.h

#pragma once

#include <ecs/config.h>

#include "./worker.h"
#include "./types.h"

beg_namespace_ecs_core_utils
{

    struct thread_pool
    {
    private:
        using worker_vector = std::vector<thread_pool_worker>;
        using atomic_size_t = std::atomic<size_t>;

    private:
        task_queue      _queue;
        worker_vector   _workers;
        atomic_size_t   _outstanding_inits;

        auto all_workers_finished() const noexcept
        {
            for (const auto& w : _workers)
            {
                if (!w.finished())
                {
                    return false;
                }
            }
            return true;
        }

        inline void post_dummy_task()
            { post([]{ }); }

        void initialize_workers(size_t count)
        {
            _workers.reserve(count);
            for (size_t i = 0; i < count; ++i)
            {
                _workers.emplace_back(_queue);
            }

            _outstanding_inits = count;
            for (auto& w : _workers)
            {
                w.start(_outstanding_inits);
            }
        }

    public:
        inline thread_pool(size_t count)
            { initialize_workers(count); }

        ~thread_pool()
        {
            // wait for uninitialized workers
            while (_outstanding_inits > 0)
            {
                std::this_thread::sleep_for(std::chrono::milliseconds(50));
            }

            // stop all workers
            for (auto& w : _workers)
            {
                w.stop();
            }

            // post dummy tasks untill all workers has stopped
            while (!all_workers_finished())
            {
                post_dummy_task();
            }

            // join the worker threads
            for (auto& w : _workers)
            {
                w.join();
            }
        }

        template<typename T_func>
        inline void post(T_func&& func)
            { _queue.enqueue(std::forward<T_func>(func)); }
    };

}
end_namespace_ecs_core_utils