GetMainThread.cpp

DWORD GetMainThread(DWORD Pid)
{
	struct
	{
		const DWORD Pid;
		DWORD Tid;
	} tmpDat = {Pid, 0};
	
	EnumWindows(
		[](HWND hWnd, LPARAM lp) -> BOOL
		{
			DWORD WndPid;
			DWORD tmpTid = GetWindowThreadProcessId(hWnd, &WndPid);
			
			auto pTmpDat = reinterpret_cast<decltype(tmpDat)*>(lp);

			if (
				WndPid == pTmpDat->Pid &&
				GetWindow(hWnd, GW_OWNER) == NULL &&
				IsWindowVisible(hWnd))
			{
				pTmpDat->Tid = tmpTid;
				return FALSE;
			}
			else
			{
				return TRUE;
			}
		},
		reinterpret_cast<LPARAM>(&tmpDat));

	return tmpDat.Tid;
}