Example of proper handling of threadstate/interplock for low level C thread

[Grant Munsey]

I read the API manual on threading and am still a little confused about
what I have to do to protect the interpreter when a low level C based
thread gets control of an app and wants to .... say do a
Py_RunSimpleString().

Can anyone point me to some source examples that handle threads that
are not started by the Python interpreter?