Seun Osewa <seun.osewa@gmail.com> writes:
> What is it about Python that makes a thread-safe CPython version much
> slower?...
> I'm thinking it might be the reference counting approach to memory
> management...

Yes. In the implementation that was benchmarked, if I understand
correctly, every refcount had its own lock, that was acquired and
released every time the refcount was modified.