Extending Cython with GIL-free types [EuroPython 2021 - Talk - 2021-07-28 - Brian] [Online] By Xavier Thompson Cython is a compiled language, largely inspired by Python, which can already provide both massive speedups and seamless interoperability with C libraries. In Cython, Python and C can freely mix thanks to a unified syntax and gradual typing. This opens the door to bypassing the GIL by restricting oneself to the C side of Cython, but it entails letting go of all the high-level semantics of Python and going back to low-level manual memory management, pointer arithmetic and good old segmentation faults... Not to mention all the joys of multi-threading in C! In this talk, we will recount how we experimentally extended Cython to bridge that gap with GIL-free reference-counted types and a type system for thread-safe concurrency. We call this extension: Cython+. By hacking a bit the Cython compiler, one can create new language features which translate under-the-hood to low-level GIL-agnostic C or C++. In this way we extended Cython with a new class system that looks familiar to a Python programmer, but can be used in Cython while the GIL is released because it does not depend on the Python/C API. By adapting the way Cython generates reference counting instructions for Python objects, we equipped our types with a thread-safe reference count. Thanks to Cython's expertise with the Python/C API, we wrapped our types into extension types, thus gaining interoperability with Python. And using Cython's static type checking, we are currently introducing an ownership type system for thread-safe concurrency inspired by Pony and Rust. License: This video is licensed under the CC BY-NC-SA 4.0 license: https://creativecommons.org/licenses/by-nc-sa/4.0/ Please see our speaker release agreement for details: https://ep2021.europython.eu/events/speaker-release-agreement/