mame-issue.cpp

bool netplay_manager::rollback(unsigned long long before_frame)
{
	if (m_debug)
	{
		NETPLAY_LOG("rollback at %llu to %llu", m_frame_count, before_frame);
	}
	
	auto sys_start_time = system_time();

	netplay_assert(before_frame <= m_frame_count); // impossible to go to the future

	// store the current time, we'll advance the simulation to it later
	auto current_frame = m_frame_count;

  // ... some more stuff happens here but it's irrelevant to the problem ...

	// let the emulator know we need to catch up
	// this should disable sound and video updates during the simulation loop below
	m_catching_up = true;

	// run the emulator loop
	// this will replay any new inputs that we have received since
	while (m_frame_count < current_frame)
	{
		auto start_time = machine().time();

		while (machine().time() < start_time + netplay_frametime)
		{
			machine().scheduler().timeslice();
		}

		m_frame_count++;
		m_machine_time += netplay_frametime;
	}

	m_catching_up = false;

	if (m_debug)
	{
		auto duration = system_time() - sys_start_time;
		NETPLAY_LOG("rollback complete at time %s and frame %llu (took %dms)",
			m_machine_time.as_string(4), m_frame_count, (int)(duration.as_double() * 1000.0));
	}

	return true;
}