[PyKDE] PyQt 3.12 introduces deadlock with QCustomEvent's destructor.

[Truls A. Tangstad]

On Mon, Aug 16, 2004 at 04:10:50PM +0100, Phil Thompson wrote:
> On Friday 06 August 2004 3:22 pm, Truls A. Tangstad wrote:
> > This problem might be somewhat related to my last post "PyQt 3.12
> > introduces race condition/deadlock with QApplication.postEvent." (see
> > [1])
> >
> > It seems that the destructor of QCustomEvent causes problems/hangs
> > just by creating an instance of it and then deleting it in a thread
> > other than the GUI/event/main-thread. This only occurs in version 3.12
> > of PyQt, and was not a problem in 3.11.
> >
> > The problem does not seem to occur when sending the event object to
> > qt.qApp.postEvent before deleting it, even when the posting function
> > should be the only one left with a reference to the object.
> >
> > One rarely creates a QCustomEvent without posting it, but the behavior
> > is still strange.
> >
> > In the enclosed example two threads are started, one creates a
> > QCustomEvent object, posts it, then deletes it, after waiting to make
> > sure the event handler is done with it. The second thread creates a
> > QCustomEvent object then deletes it, causing the application to hang
> > with PyQt 3.12.
> >
> > I'm running on Debian Unstable using the following package versions:
> > libqt3c102-mt       3.2.3-4
> > python2.3-qt3       3.12-1
> > python2.3-sip4-qt3  4.0-2
> >
> > [1] http://mats.imk.fraunhofer.de/pipermail/pykde/2004-August/008303.html

> Please read the PyQt documentation regarding using the Python thread module 
> with PyQt - you aren't following the guidelines.
> 
> Attached is a version of your script which uses QThread instead and seems to 
> work fine.

Thanks for clearing that up! It's been giving us quite a hassle, but
replacing pythons thread with QThread seems to have been a solution.
Reading the right piece of documentation is always a good idea.

It's a hard pill to swallow though, since this means our application
will have to be infected with Qt in layers not at all related to GUI,
just because GUI components can register callbacks etc. in them.

-- 
Truls A. Tangstad - <kerfue+pykde at h e r o c a m p.org>