BUG: Reference cycle problem with multiple windows open about pyvistaqt

[GuillaumeFavelier]

Could it be related to pyvista _ALL_PLOTTERS variable? What happens if you try pyvista.close_all() at the end of the script?

[larsoner]

Same result (testing the PyVista minimal example, not the MNE ones, though I'm confident they will behave the same way):

[GuillaumeFavelier]

I tried resolving some reference cycles (decreasing the reference count: self.interactor, self.frame, self.app_window, ...), I tried force-freeing Qt objects (deleteLater() and sip.delete()). I also looked at QVTKRenderWindowInteractor, I tried the same approach with ref count (_Iren, _RenderWindow), explicitly deleting _hidden widget and calling (again) Finalize() to free vtk items.

What I did not try is to decrease the ref count of callables. From stackoverflow:

Note that when it comes to signal/slot connections, PyQt treats wrapped C++ slots and Python instance methods differently. The reference counts of these types of callable are not increased when they are connected to signals, whereas lambdas, defined functions, partial objects and static methods are. This means that if all other references to the latter types of callable are deleted, any remaining signal connections will keep them alive. Disconnecting the signals will allow such connected callables to be garbage-collected, if necessary.

I did not notice any significant improvement. Do you have any ideas @pyvista/developers ?

[GuillaumeFavelier]

I think #66 could help with this especially if a test is designed for it. I'll do my best to go back on it when I can to make it move forward 👍

[larsoner]

Pretty sure this is VTK+Qt's problem, not PyVista's. :(

Closing for https://gitlab.kitware.com/vtk/vtk/-/issues/18588 but I'll try to remember to report back here if it's ever fixed