/*
 * Modern effects for a modern Streamer
 * Copyright (C) 2020 Michael Fabian Dirks
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
*/

#include "util-threadpool.hpp"
#include <cstddef>

// Most Tasks likely wait for IO, so we can use that time for other tasks.
#define CONCURRENCY_MULTIPLIER 2

util::threadpool::threadpool() : _workers(), _worker_stop(false), _tasks(), _tasks_lock(), _tasks_cv()
{
	std::size_t concurrency = static_cast<size_t>(std::thread::hardware_concurrency() * CONCURRENCY_MULTIPLIER);
	for (std::size_t n = 0; n < concurrency; n++) {
		_workers.emplace_back(std::bind(&util::threadpool::work, this));
	}
}

util::threadpool::~threadpool()
{
	_worker_stop = true;
	_tasks_cv.notify_all();
	for (auto& thread : _workers) {
		_tasks_cv.notify_all();
		if (thread.joinable()) {
			thread.join();
		}
	}
}

std::shared_ptr<::util::threadpool::task> util::threadpool::push(threadpool_callback_t fn, threadpool_data_t data)
{
	auto task = std::make_shared<util::threadpool::task>(fn, data);

	std::unique_lock<std::mutex> lock(_tasks_lock);
	_tasks.emplace_back(task);
	_tasks_cv.notify_one();

	return task;
}

void util::threadpool::pop(std::shared_ptr<::util::threadpool::task> work)
{
	if (work) {
		work->_is_dead.store(true);
	}
}

void util::threadpool::work()
{
	static thread_local std::shared_ptr<util::threadpool::task> local_work{};

	while (!_worker_stop) {
		// Wait for more work, or immediately continue if there is still work to do.
		{
			// Lock the tasks mutex to check for work.
			std::unique_lock<std::mutex> lock(_tasks_lock);

			// If there are currently no tasks queued, wait on the condition variable.
			// This temporarily unlocks the mutex until it is woken up.
			if (_tasks.size() == 0) {
				_tasks_cv.wait(lock, [this]() { return _worker_stop || _tasks.size() > 0; });
			}

			// If there is either no tasks or we were asked to stop, skip everything.
			if (_worker_stop || (_tasks.size() == 0)) {
				continue;
			}

			// Grab the latest task and immediately remove it from the queue.
			local_work = _tasks.front();
			_tasks.pop_front();
		}

		// If the task was killed, skip everything again.
		if (local_work->_is_dead.load()) {
			continue;
		}

		// Try to execute work, but don't crash on catchable exceptions.
		if (local_work->_callback) {
			try {
				local_work->_callback(local_work->_data);
			} catch (std::exception const& ex) {
			} catch (...) { // This does not catch unrecoverable exceptions, or exceptions that went through C code.
			}
		}
	}
}

util::threadpool::task::task() {}

util::threadpool::task::task(threadpool_callback_t fn, threadpool_data_t dt) : _callback(fn), _data(dt), _is_dead(false)
{}