Stopping main program flow while a handler is active

if you know the max waiting time for the popup, then this would do the job:

(1)def myHandler(event):
(2) #code to make popup vanish
(3) event.region.stopObserver()

(4)def func():
(5) #Main Function code
(6) onAppear(pImage, myHandler)
(7) observe(5)
(9) #Continue with main function

Now you are using the inline observe, which would continue with (9) immediately after the popup appeared but max 5 seconds (if not).

usually one cannot really proceed with the main workflow while having the risk of a popup.
But if it is possible in your case:
(1)def myHandler(event):
(2) #code to make popup vanish
(3) event.region.stopObserver()

(4)def func():
(5) #Main Function code
(6) onAppear(pImage, myHandler)
(7) observe(5,background=True)
(9) #Continue with main function

it continues immediately after (7), since the observe is done in parallel and stopped after 5 seconds anyway.

If you can somehow foresee the popup situation, this would be also possible (no use of observe):

** not needed (1)def myHandler(event):

(4)def func():
(5) #Main Function code
if popupMightAppear:
    if exists(pImage, 5):
        #code to make popup vanish
(9) #Continue with main function

Be aware: up to version 1.0.1 the observe feature has many quirks and the most critical is, that mouse and keyboard usage is not coordinated between main workflow and handler in case of background=true, which might lead to strange situations.

with version 1.1.0+ mouse/keyboard usage is coordinated between threads.
Additionally for critical sections it is possible to reserve the usage for one thread.
The background observe will have a feature to check in main workflow wether the observed events have already happened, which allows, to have the handling inline (no handler might be needed) at various places in the workflow, which is the best way to coordinate.

Thanks Raiman! A simple solution that I was too muddled up to see.