well, your second sentence immediately makes untrue first sentence :)

No offence!
Yet I appplause very much your effort with Marrying Tk, threads and SerialPort - a COM port monitor.

But you either "nothing to fear of", or "not trivial" (meaning you must take special care of threading, especially coonsidering weak internal threads in perl, so you must always switch to OS API for reliable threads)

As to add a little bit, Tcl::Tk is more lightweight than Tk , so your experiments on trying Tk to have less CPU cycles (as to allow more COM processing) are better done with Tcl::Tk.