Sequential programming, threads, causality, and the nature of time

q&a
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Hi guys!

I just started with PyQt and it seems pretty cool but tried to use a “progress bar” to track a long i/o process which introduced me to threads. I have things mostly working and understand how a long i/o would mess up the event queue for functions called AFTER the i/o process is called but I have experienced the following:

  1. FIRST I try & update some GUI widgets
  2. Immediately AFTERWARDS I call the long i/o function

Somehow step #2 interferes with step #1! It’s like a time machine! :wink:
I’m guessing that the call to step #1 just places GUI commands in a queue which immediately gets interfered with by step #2? So… I guess all I’m asking for is a way to “flush the queue” or somehow force step #1 to complete before step #2? I tried calling various “update” & “repaint” functions but that doesn’t seem to help.
I can (of course) deal with this via threads but it seems a bit inelegant…
Any suggestions?

TIA,
Dan

2

Qt always runs application logic before it runs UI code, even if Ui code was called first, that is what is going on.

To fix this call the I/O function in a separate thread.

3

Hello, @SAMBERPE10683, welcome to the forum! :slightly_smiling_face:

Yeah, do what @amohgyebigodwin10691 said. @martin has written a wonderful article on this topic. You’ll find all your answers there.

1 Like
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Thanks!
It really is an excellent article.