[Interest] Annoying Bug - Qt 4.8.1 bug?

[Bo Thorsen]

Den 23-01-2014 10:15, Etienne Sandré-Chardonnal skrev:
> Dear all,
>
> I'm tracking a bug since a few days, which happens at the end of file
> saving in my app. It saves using a separate thread, while the GUI
> displays a modal progress dialog. The app crashes in the QProgressDialog
> destructor, and this does not happen all the time. I have double checked
> that the destructor is called only once; it's allocated on the heap and
> I let Qt destroy it with the flag WA_DeleteOnClose.
>
> I spent a few hours stripping my app to the bare minimum that keeps it
> crashing. The good news is that it's possible to reproduce it with a
> small project, the bad is the probability for crashing at each click on
> the "save" button decreases when the GUI becomes simple (I had to keep a
> few widgets and UI to keep it at a detectable level) but everything is
> made with .ui's and generated by Qt, so my code is minimal. You may find
> the project attached, I'm running Qt 4.8.1 under win7 64 bit, with
> mingw32 and mingw64 (both crash). *To trigger the crash, you need to
> click on "Save" toolbutton, then press enter. This needs to be repeated
> several times, several varying between 2 and 50.*

Hi Etienne,

I took a look at your code, and unfortunately there is a lot wrong with it.

Your BackgroundFileWorker class does not run the a separate thread. You 
don't call start() and the run() method is empty so it returns immediately.

And you don't even need a thread for this. Create the progress dialog 
and do a loop that does something like this:

while not done
   save a chunk
   update the progress dialog
   QApplication::processEvents()

I can guarantee you there is no Qt bug here.

One thing I would advise you: Stop creating all those objects on the 
heap. Create them on the stack instead whenever you can. For example, 
the saveSceneDialog shouldn't be a new SaaveSceneDialog().

Get rid of the threads and try again.

Bo.

-- 
Bo Thorsen, European Engineering Manager, ICS
Integrated Computer Solutions. Delivering World-Class Applications
http://ics.com/services