gzdoom-gles/src/r_thread.cpp

#include <stddef.h>
#include "templates.h"
#include "doomdef.h"
#include "i_system.h"
#include "w_wad.h"
#include "r_local.h"
#include "v_video.h"
#include "doomstat.h"
#include "st_stuff.h"
#include "g_game.h"
#include "g_level.h"
#include "r_thread.h"

CVAR(Bool, r_multithreaded, true, CVAR_ARCHIVE | CVAR_GLOBALCONFIG);

void R_BeginDrawerCommands()
{
	DrawerCommandQueue::Begin();
}

void R_EndDrawerCommands()
{
	DrawerCommandQueue::End();
}

/////////////////////////////////////////////////////////////////////////////

DrawerCommandQueue *DrawerCommandQueue::Instance()
{
	static DrawerCommandQueue queue;
	return &queue;
}

DrawerCommandQueue::DrawerCommandQueue()
{
}

DrawerCommandQueue::~DrawerCommandQueue()
{
	StopThreads();
}

void* DrawerCommandQueue::AllocMemory(size_t size)
{
	// Make sure allocations remain 16-byte aligned
	size = (size + 15) / 16 * 16;

	auto queue = Instance();
	if (queue->memorypool_pos + size > memorypool_size)
		return nullptr;

	void *data = queue->memorypool + queue->memorypool_pos;
	queue->memorypool_pos += size;
	return data;
}

void DrawerCommandQueue::Begin()
{
	auto queue = Instance();
	queue->Finish();
	queue->threaded_render++;
}

void DrawerCommandQueue::End()
{
	auto queue = Instance();
	queue->Finish();
	if (queue->threaded_render > 0)
		queue->threaded_render--;
}

void DrawerCommandQueue::WaitForWorkers()
{
	Instance()->Finish();
}

void DrawerCommandQueue::Finish()
{
	auto queue = Instance();
	if (queue->commands.empty())
		return;

	// Give worker threads something to do:

	std::unique_lock<std::mutex> start_lock(queue->start_mutex);
	queue->active_commands.swap(queue->commands);
	queue->run_id++;
	start_lock.unlock();

	queue->StartThreads();
	queue->start_condition.notify_all();

	// Do one thread ourselves:

	DrawerThread thread;
	thread.core = 0;
	thread.num_cores = (int)(queue->threads.size() + 1);

	for (int pass = 0; pass < queue->num_passes; pass++)
	{
		thread.pass_start_y = pass * queue->rows_in_pass;
		thread.pass_end_y = (pass + 1) * queue->rows_in_pass;
		if (pass + 1 == queue->num_passes)
			thread.pass_end_y = MAX(thread.pass_end_y, MAXHEIGHT);

		size_t size = queue->active_commands.size();
		for (size_t i = 0; i < size; i++)
		{
			auto &command = queue->active_commands[i];
			command->Execute(&thread);
		}
	}

	// Wait for everyone to finish:

	std::unique_lock<std::mutex> end_lock(queue->end_mutex);
	queue->end_condition.wait(end_lock, [&]() { return queue->finished_threads == queue->threads.size(); });

	// Clean up batch:

	for (auto &command : queue->active_commands)
		command->~DrawerCommand();
	queue->active_commands.clear();
	queue->memorypool_pos = 0;
	queue->finished_threads = 0;
}

void DrawerCommandQueue::StartThreads()
{
	if (!threads.empty())
		return;

	int num_threads = std::thread::hardware_concurrency();
	if (num_threads == 0)
		num_threads = 4;

	threads.resize(num_threads - 1);

	for (int i = 0; i < num_threads - 1; i++)
	{
		DrawerCommandQueue *queue = this;
		DrawerThread *thread = &threads[i];
		thread->core = i + 1;
		thread->num_cores = num_threads;
		thread->thread = std::thread([=]()
		{
			int run_id = 0;
			while (true)
			{
				// Wait until we are signalled to run:
				std::unique_lock<std::mutex> start_lock(queue->start_mutex);
				queue->start_condition.wait(start_lock, [&]() { return queue->run_id != run_id || queue->shutdown_flag; });
				if (queue->shutdown_flag)
					break;
				run_id = queue->run_id;
				start_lock.unlock();

				// Do the work:
				for (int pass = 0; pass < queue->num_passes; pass++)
				{
					thread->pass_start_y = pass * queue->rows_in_pass;
					thread->pass_end_y = (pass + 1) * queue->rows_in_pass;
					if (pass + 1 == queue->num_passes)
						thread->pass_end_y = MAX(thread->pass_end_y, MAXHEIGHT);

					size_t size = queue->active_commands.size();
					for (size_t i = 0; i < size; i++)
					{
						auto &command = queue->active_commands[i];
						command->Execute(thread);
					}
				}

				// Notify main thread that we finished:
				std::unique_lock<std::mutex> end_lock(queue->end_mutex);
				queue->finished_threads++;
				end_lock.unlock();
				queue->end_condition.notify_all();
			}
		});
	}
}

void DrawerCommandQueue::StopThreads()
{
	std::unique_lock<std::mutex> lock(start_mutex);
	shutdown_flag = true;
	lock.unlock();
	start_condition.notify_all();
	for (auto &thread : threads)
		thread.thread.join();
	threads.clear();
	lock.lock();
	shutdown_flag = false;
}