Only mainloop is mainloop, mainloop is drawing the gui, responding to events ... without mainloop you have to ->show/->update/->dooneevent ... its FAQ Re^3: Perk Tk - how to send a value from a subroutine back to the main program using Button This might help :) Re: Win32::GUI window freezing, even with threading. (win32-gui-tk-thread-dequeue.pl, Thread::Queue::popnow/push) + Re^4: Win32::GUI window freezing, even with threading. (Wrong solution)