Display a label while pressing the button in my GUI

[Peter Otten]

Peter Otten wrote:

> PS: You can verify that you understood this by answering the question:
> what happens if the user hits the go-button while the second thread is
> still running. Hint: as written the script does not handle this correctly.

On second thought it's probably not as bad as I thought when I wrote the 
above. I assumed that the messages after the first "done" would remain in 
the queue forever, but there is another independent check_state() invocation 
that should read the rest.
I hope ;)