As you stated on Stackoverflow, the fact that the function `A.f` becomes the function `B.f` after a pickling-unpickling sequence creates an infinite recursive call of `B.f` in worker processes started with `multiprocessing.pool.Pool().apply(super().f)` or `concurrent.futures.ProcessPoolExecutor().submit(super().f)` in `B.f` where B is a subclass of A. This infinite recursion has crashed my laptop several times today, so it looks like it is a rather critical issue.