Don't bother disconnecting signals in TimerQt.__del__. #8450
Conversation
The current implementation sometimes raises an error at exit. For
example, run `examples/animations/animate_decay.py` (under the
Qt5Agg backend) and wait after the x-axis has been updated at least
once; then close the window. *Occasionally*, the following error will
be printed at exit:
```
Exception ignored in: <bound method TimerQT.__del__ of <matplotlib.backends.backend_qt5.TimerQT object at 0x7f74a65f5668>>
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/matplotlib/backends/backend_qt5.py", line 202, in __del__
self._timer.timeout.disconnect(self._on_timer)
TypeError: 'method' object is not connected
```
As far as I can tell there is no real rationale for bothering to
explicitly disconnect the callback -- the C++-level QTimer object is
about to be garbage-collected anyways.
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Does this prevent a circular set of references? Nominally 👍 but want to think a bit more. |
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The C++-level QTimer object keeps a reference to self._on_timer whereas the Python-level TimerQt object keeps a reference to the QTimer, so there is already a circular ref in the way the class is designed. If we manage to reach a point where |
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Hurray for GC race-conditions! I am leaning a bit towards simply swallowing the TypeError exception. What if we redesign the class to no longer have the cyclic reference? Then we would need the |
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note, I am not suggesting that we redesign the class, just simply saying that if in the future the class gets redesigned, one may forget to add back the |
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I don't understand the insistence on keeping del. |
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There's no need to disconnect here, I think I was just being way overly cautious. Qt disconnects in destructors at the C++ level. |
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Going to backport this |
…merqt-__del__ MNT: Don't bother disconnecting signals in TimerQt.__del__.
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backported to v2.0.x as b160593 |
The current implementation sometimes raises an error at exit. For
example, run
examples/animations/animate_decay.py(under theQt5Agg backend) and wait after the x-axis has been updated at least
once; then close the window. Occasionally, the following error will
be printed at exit:
As far as I can tell there is no real rationale for bothering to
explicitly disconnect the callback -- the C++-level QTimer object is
about to be garbage-collected anyways.