Find GUI thread

gui_threads.cpp

HANDLE find_thread(HANDLE hProcess, DWORD thAccess, bool guiOnly)
{
	DWORD targetPid = GetProcessId(hProcess);
	HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0);
	THREADENTRY32 thEntry = { sizeof(THREADENTRY32) };

	GUITHREADINFO gui = { 0 };
	gui.cbSize = sizeof(GUITHREADINFO);

	bool isGUIProcess = false;
	DWORD  uiFlags = 0;
	if (GetGuiResources(hProcess, uiFlags)) {
		isGUIProcess = true;
		std::cout << "The process is GUI\n";
	} else if (guiOnly) {
		std::cout << "The process is not GUI\n";
		return NULL;
	}

	std::vector<DWORD> threads;
	if (Thread32First(snapshot, &thEntry)) {
		do {
			if (thEntry.th32OwnerProcessID == targetPid) {
				if (isGUIProcess) {
					if (!GetGUIThreadInfo(thEntry.th32ThreadID, &gui)) {
						continue;
					}
					std::cout << "GUI thread: " << thEntry.th32ThreadID << "\n";
				}
				threads.push_back(thEntry.th32ThreadID);
			}
		} while (Thread32Next(snapshot, &thEntry));
	}
	CloseHandle(snapshot);

	for (auto itr = threads.begin(); itr != threads.end(); ++itr) {
		DWORD threadId = *itr;
		HANDLE hThread = OpenThread(thAccess, FALSE, threadId);
		if (!hThread || hThread == INVALID_HANDLE_VALUE) {
			continue;
		}
		return hThread;
	}
	return NULL;
}