Panda3d crashes when setting threading model (only python 3.9)

[thomassedlmayer]

I was experiencing crashes with panda3d (any newer version), kivy (tested 2.1.0, 2.0.0) and panda3d_kivy (0.3.0, 0.4.0) when running my application with python 3.9 (tested 3.9.5, 3.9.12). Everything worked just fine with python 3.7.5. Unfortunately, I wasn't getting any sensible logging output since it just crashed without any warning.

Though, I found out that these crashes are related to a custom threading model that is set in my application (e.g., loadPrcFileData('', "threading-model cull/draw" or loadPrcFileData('', "threading-model Cull")).

Does anyone know if this can be fixed? I think this bug is at least somehow related to panda3d-kivy because I do not get crashes when removing all panda3d-kivy-related imports. The app even crashes when I do not add anything but imports.