[PyQt] Long running processes, threads, progress dialog

[Catriona Johnson]

>On Thursday 24 March 2011, 02:00:03 Catriona Johnson wrote:
>> >> Hello
>> >>
> >>> I have a GUI application that occasionally has a number of long
> >>> running processes - eg data deletions , html report generation.
> >>>
> >>> I have a custom progress widget that displays a spinning icon (my
> >>> client didn't like the Qt QProgressDialog) which I display during
>> >>long running processes - the user doesn't need to be able to
>> >> interact with the GUI while this is happening.
>> >>
>> >> I have started to implement a worker thread to perform these long
>> >> running processes. My question is do I initiate each process from
>> >> the Thread's run method as follows or does each operation have its
>> >> own thread ?? Do I need to use a secondary thread at all? Is there
>> >> a better way ??
>> >>
> >>> def run(self):
> >>>               if self.operation == A_DELETE:
> >>>                       self.completed =
> >>> AModel.model().removeRecord(self.identity) elif self.operation ==
> >>> B_DELETE:
> >>>                       self.completed =
> >>> BModel.model().removeRecord(self.identity) elif self.operation ==
> >>> REPORTS:
> >>>                       self.completed =
> >>> ReportWriter.generateReport() self.stop()
> >>>               self.emit(SIGNAL("finished(bool)"), self.completed)
> >>>               self.wait()
> >>
> >>You may want to read this article, which is mostly valid also for
> >> PyQt:
> >>
> >>       http://www.linuxjournal.com/article/9602
> >>
> >>From a PyQt POV and depending on where the action is, the presence
> >> of the GIL might want to be taken into account..
> >>
> >>Pete
>>
>> Thanks for that Pete - it is a good article.
>>
>> My case is not that complicated though. I am reading and sometimes
>> updating binary files that contain the data for the application.
>> These processes are never concurrent and do not connect to a
>> database. My understanding is from the article that each process has
>> a thread and the process is run from the thread's run method?

>Hmm, every process _is_ a thread (in the sense of an execution unit).
>Since that cannot be stopped easily (apart from termination), there's
>no run method involved. That comes into play, if threads enter the
>picture. For every running thread (one, that got its start method
>called), your process grows another execution unit, but these need some
>preparation and following special rules, as the article shows.

>> Implementing threading does seem a little bit of overkill if all I
>> want is a modal progress dialog to display while the operation is
>> occurring. What is the best way to do it.
>>
>> I did try a QProgressDialog as follows but although it was displayed
>> there was no animation. I want an indeterminate progress bar
>>
>> progressDialog = QProgressDialog()
>> progressDialog.setMinimum(0)
>> progressDialog.setMaximum(0)
>> progressDialog.setValue(-1) # As set in Designer
>> progressDialog.show()

>Ahh, I didn't understand your issue.

>Try calling QtGui.QApplication.processEvents() periodically in the
>loops, but note, that calling this method has to be done from the UI
>thread, e.g. the one, that called QtGui.QApplication() before.

>Pete

Thanks for that, I will give it a go.

Catriona