Support free-threaded Python 3.13 build

[ngoldbaum]

Is your feature request related to a problem?

Python 3.13 will be available as an experimental free-threaded build that has the GIL disabled. It should hopefully be possible to build aiohttp on the free-threaded build with an updated Cython. I just did so (with some makefile hacking so the build uses a prerelease cython):

Python 3.13.0rc1 experimental free-threading build (main, Aug 14 2024, 13:20:46) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import aiohttp
<frozen importlib._bootstrap>:488: RuntimeWarning: The global interpreter lock (GIL) has been enabled to load module 'aiohttp._helpers', which has not declared that it can run safely without the GIL. To override this behavior and keep the GIL disabled (at your own risk), run with PYTHON_GIL=0 or -Xgil=0.

Describe the solution you'd like

I don't know what thread safety issues exist in aiohttp, but assuming any C/C++ code is thread safe and the cython code is thread safe, you can declare the modules support free-threading by following https://py-free-threading.github.io/porting/.

Describe alternatives you've considered

Not supporting it?

Related component

Server, Client

Additional context

No response

Code of Conduct

• I agree to follow the aio-libs Code of Conduct

[Dreamsorcerer]

If you'd like to help, I think the first thing would be to add a new test run to the CI, so we have some test coverage over this new approach. But, I'd assume the Cython code is likely thread-safe as it's just used for parsers.

Probably need the current 3.13 tests passing first though, which will hopefully happen next week after uvloop publish a 3.13 wheel.

[webknjaz]

I think that getting our in-org hosted deps to run CI / make builds might be another blocker. I think that aiohttp's CI should make use of those wheels rather than compiling them.

[Dreamsorcerer]

3.13 is fully tested and passing now, if anyone wants to look at adding the free-threading testing.