C extension/multithreading question

[David Rushby]

Is it safe to call PyThread_acquire_lock and PyThread_release_lock on
a PyThread_type_lock from a native thread that:
a) was not created by Python
b) has no bootsrapped Python thread state
c) does not have the GIL locked
?

It appears that this is safe, since the GIL itself is of type
PyThread_type_lock, but I want to make sure that I'm not missing some
fatal subtlety.

Thanks.