user interface - Should I use QCoreApplication::processEvents() or QApplication::processEvents()?

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I have a method which is called from both QThreads and the main thread. this method can sometimes take a long time to do its computations in a loop so I put QCoreApplication::processEvents() and this prevents the GUI from freezing. At some point I had changed QCoreApplication::processEvents() for QApplication::processEvents() but that caused the GUI to freeze (im pretty sure thats what was fereezing it because since I put QCoreApplication::processEvents() back it hasnt frozen again) Am I right to think that calling QApplication::processEvents() from both the main thread and QThreads can freeze the GUI?

Neither, processEvent() should be calld only when you have actual pending events to process. You may find this useful : How to make Qt work when main thread is busy?

I am going to try QtConcurrent::run. Can I do GUI operations in there or should I still emit signals like for the case of a QThread – yan bellavance Jan 28, 2010 at 1:05 @yan bellavance: You should emit signals, as it will be in a separate thread. Or you could use the QFuture stuff to help, which will do a lot of creating and emitting the signals for you. – Caleb Huitt - cjhuitt Jan 28, 2010 at 19:27

You'll be much better off moving the long-running process out of the main thread so you don't need to call processEvents() . Within that long-running process, you can emit whatever signals you need so the gui has sufficient information to do updates, etc. processEvents , however, is usually a crutch for a poor design.

I am going to try QtConcurrent::run. Can I do GUI operations in there or should I still emit signals like for the case of a QThread – yan bellavance Jan 28, 2010 at 1:30 Gui operations may only be performed in the main thread. QtConcurrent is a good idea, especially if you can divide your work up to utilize multiple cores. – Kaleb Pederson Jan 28, 2010 at 17:08

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