[PyQt] Segfault with 5.9 snapshot when connecting to destroyed signal

[Florian Bruhin]

Hi,

On Tue, Jun 06, 2017 at 03:34:12PM +0100, Phil Thompson wrote:
> On 5 Jun 2017, at 10:42 pm, Florian Bruhin <me at the-compiler.org> wrote:
> > the attached script works fine with PyQt 5.8, but segfaults with the
> > current 5.9 snapshot. This is a simplified version of pytest-qt's
> > SignalBlocker: http://pytest-qt.readthedocs.io/en/latest/signals.html
> > 
> > The "self.args = args" saves a reference to the to-be-destroyed object,
> > which probably triggers this in some way - saving the arguments is done
> > as a general thing here though. It's probably a bit unorthodox, but
> > still shouldn't segfault I guess?
> 
> Should be fixed in tonight's PyQt snapshot.
> 
> Current snapshots have additional code to detect when certain objects
> get destroyed. This is deceptively difficult to get right (as you have
> found). I'd appreciate any testing you can do with the snapshots
> before the v5.9 release.

The segfault is gone, and I didn't notice any new issues, however...

On Tue, Jun 06, 2017 at 04:28:56PM +0100, Phil Thompson wrote:
> > Thanks! Another thing I've noticed is with code like this:
> > 
> >    class NetworkManager(QNetworkAccessManager):
> > 
> >        def __init__(self, parent=None):
> >            super().__init__(parent)
> >            self._replies = []
> > 
> >        def createRequest(self, *args):
> >            reply = super().createRequest(*args)
> >            self._replies.append(reply)
> >            reply.destroyed.connect(self._requests.remove)
> >            return reply
> > 
> > I suddenly got "ValueError: list.remove(x): x not in list" with the
> > snapshot which I didn't with 5.8.
> > 
> > I ended up just removing[1] that reply tracking because I didn't need it
> > anymore, but now I wonder whether that's expected. I'm guessing the
> > argument of the destroyed signal doesn't compare equal to what I
> > stored earlier anymore?
> > 
> > Let me know if you need a minimal example and I'll see if I can write one.
> 
> Try it again with tonight's snapshot.
> 
> As far as PyQt is concerned the destroyed() signal is evil. This would
> be a lot easier if you ask a QObject if it was being destroyed.

...this is still an issue. I haven't really done any further
investigation though.

Florian

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