// A global bool end;

		while (CommPort.ReadDataWaiting() ) {
		    if(end) break;
                        ...
                    Sleep(980);
                    ....

	void Exit0() {
           end = true; Sleep(2000);
	   if(CommPort.IsOpened()) CommPort.Close();
	   if(CommPort2.IsOpened()) CommPort2.Close();
	   Thread::ShutdownThreads();
	   Break(); // Closes window with 'Cancel'
	}	
void endX(){end = true;	Sleep(2000);}	

GUI_APP_MAIN{
    GPSv2().Run();
    endX();
    if(CommPort.IsOpened()) CommPort.Close();
    if(CommPort2.IsOpened()) CommPort2.Close();
    Thread::ShutdownThreads();
}