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

[Florian Bruhin]

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:
> > 
> > Hi,
> > 
> > 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.

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.

Other than that, my (pretty big) testsuite for qutebrowser[2] passed
fine.

[1] https://github.com/qutebrowser/qutebrowser/commit/a45de9cef2f8c292d42aa4f63bf6a1ea08557508
[2] https://qutebrowser.org/

Florian

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