MainWindow update during computations

**gfunk** · 13th July 2006, 19:09

Originally Posted by Gizmho

Does the call processEvents() slow down the application?

Probably just the price of a function call, multiplied by how many times you need to call it, as well as the cost of processing the events. But that's just the price of having your application "feel" like it's doing multitasking and being responsive. You can't get things for free. For the most part, the performance drop should be negligible.

**aMan** · 13th July 2006, 19:39

how does this handle the following thing:

Qt Code:

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computing very much A
break -> processEvents()
   compute something
   compute something
   compute very much B
continue with A
computing very much A
..

computing very much A
break -> processEvents()
   compute something
   compute something
   compute very much B
continue with A
computing very much A
..

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will A continue only after B is finished?
so when i call A in B, then i'll get a recursion?

regards..
aman..

**gfunk** · 13th July 2006, 19:56

Yes, according to the docs, processEvents() processes all pending events before returning - all this work is done in the same thread. So, if function A() calls processEvents(), and one of the event handlers (perhaps B()) then calls A() again, there might be some recursion. I don't think it would be infinite recursion; the event being processed must be removed from the list of pending events before getting processed, and it looks like Qt follows this at least in Windows (in qeventdispatcher_win.cpp):
msg = d->queuedUserInputEvents.takeFirst();

The funny result is that events might be processed in reverse order as it finishes its recursion; but the processing should go on as the pending event list is whittled away.