3.4 Extension Modules in Subinterpreters

While subinterpreters have been a part of CPython nearly as long as extension modules, the latter have had issues dealing with the former nearly since the beginning.

• PEP 489
• https://mail.python.org/pipermail/import-sig/2015-July/001035.html

Challenges

C global state

...in extensions and libraries

pyca/cryptography #2299: C extension init races under subinterpreters

C-API

e.g. GILState API