[PyQt] hang in pyqt5.7

[oliver]

I am exploring how deleteLater, connections, QObject trees and circular
references interact (because of a bug in our pyqt 5.7 app -- I think it
might be due to strong references between some qobjects). Just want to
bring to people's attention a hard lesson learnt:  if you override
disconnectNotify(self, method) from QObject, so that you can check when
signals of self get disconnected, beware that self self.receivers() may
cause hangs. I have the following code:

def disconnectNotify(self, method):
    meth_name = bytes(method.name()).decode()
    signal = getattr(self, meth_name)
    num_receivers = self.receivers(signal)  # ***

which gets called because qobjectA.signal is connected to
qobjectB.some_slot, and qobjectB gets destroyed (so Qt automatically
disconnects signal). Oddly, the problem is the last line (***): when that
line is commented out, I can run 10,000 tests without hanging; with it,
test will hang about 1% of time.

I must say, if there is one thing that I really wish in PyQt, it's ability
to interrogate a signal for connections to find the slots (i.e. object
methods and functions) connected to it. Of course in a bug-free program,
you should never need this because the Observer pattern encourages
annonymity of emitters and receivers, but once in a while it would be
really nice to be able to check what is connected (because some connections
get established only in some circumstances, and sometimes you need to check
if a slot is still connected). Being able to do something like this when
some_signal is a pyqtSignal():

assert self.some_signal.is_connected(some_object.slot)
assert self.some_signal.num_connections < 5

would be great. Any chance of extending PyQt to support that?
Oliver
-- 
Oliver
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