Currently, tree, node and socket types are always freed immediately when the
Python code unregisters them. This is problematic, because there may still be
references to those type pointers in evaluated data owned by potentially various
depsgraphs. It's not possible to change data in these depsgraphs, because they
may be independent from the original data and might be worked on by a separate
thread. So when the type pointers are freed directly, there will be a lot of
dangling pointers in evaluated copies. Since those are used to free the nodes,
there will be a crash when the depsgraph updates. In practice, this does not
happen that often, because typically custom node tree addons are not disabled
while in use. They still used to crash often, but only when Blender exits and
unregisters all types.
The solution is to just keep the typeinfo pointers alive and free them all at
the very end. This obviously has the downside that the list of pointers we need
to keep track of can grow endlessly, however in practice that doesn't really
happen under any normal circumstances.
I'm still getting some other crashes when enabling/disabling Sverchok while
testing, but not entirely reliably and also without this patch (the crash there
happens in RNA code). So some additional work will probably be needed later to
make this work properly in all cases.
Pull Request: https://projects.blender.org/blender/blender/pulls/134360
Main goals of this refactor:
* Make it more obvious which update function should be used.
* Make it more obvious which parameters are required by using references instead
of pointers.
* Support passing in multiple modified trees instead of just a single one.
No functional changes are expected.
Pull Request: https://projects.blender.org/blender/blender/pulls/132862
