Free-threaded CPython support

[aslangencer]

I attempted to compile av for the free-threaded CPython (cpython-3.13.0+freethreaded-linux-x86_64-gnu) both with and without the LDFLAG --no-build-isolation but both attempts failed with the following error:

clang -pthread -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall -fPIC -O0 -Wno-incompatible-pointer-types -Wno-unreachable-code -fPIC -g -Iav/filter -I/usr/include/x86_64-linux-gnu -I/dev/shm/new_proj/.venv/include -I/home/testuser/.local/share/uv/python/cpython-3.13.0+freethreaded-linux-x86_64-gnu/include/python3.13t -c src/av/filter/loudnorm.c -o build/temp.linux-x86_64-cpython-313t/src/av/filter/loudnorm.o
src/av/filter/loudnorm.c:2751:80: error: unknown type name '__pyx_vectorcallfunc'; did you mean 'vectorcallfunc'?
 2751 | static CYTHON_INLINE PyObject *__Pyx_PyVectorcall_FastCallDict(PyObject *func, __pyx_vectorcallfunc vc, PyObject *const *args, size_t nargs, PyObject *kw);
      |                                                                                ^~~~~~~~~~~~~~~~~~~~
      |                                                                                vectorcallfunc

I have numpy 2.1.3 in this venv. Any ideas how to resolve this error?
Any suggestions?

[WyattBlue]

I don't think Cython supported free thread mode yet

[ngoldbaum]

It looks like av builds with Cython 3.1b1 and Python 3.13.3t:

goldbaum at Nathans-MBP in ~/Documents/free-threaded-compatibility on swig-update
(.venv) ± pip install setuptools
Collecting setuptools
  Using cached setuptools-79.0.0-py3-none-any.whl.metadata (6.5 kB)
Using cached setuptools-79.0.0-py3-none-any.whl (1.3 MB)
Installing collected packages: setuptools
Successfully installed setuptools-79.0.0

goldbaum at Nathans-MBP in ~/Documents/free-threaded-compatibility on swig-update
(.venv) ± pip install -i https://pypi.anaconda.org/scientific-python-nightly-wheels/simple cython
Looking in indexes: https://pypi.anaconda.org/scientific-python-nightly-wheels/simple
Collecting cython
  Downloading https://pypi.anaconda.org/scientific-python-nightly-wheels/simple/cython/3.1.0b1/cython-3.1.0b1-py3-none-any.whl (1.2 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 1.2/1.2 MB 4.2 MB/s eta 0:00:00
Installing collected packages: cython
Successfully installed cython-3.1.0b1

goldbaum at Nathans-MBP in ~/Documents/free-threaded-compatibility on swig-update
(.venv) ± pip install av --no-build-isolation
Collecting av
  Using cached av-14.2.0.tar.gz (4.1 MB)
  Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: av
  Building wheel for av (pyproject.toml) ... done
  Created wheel for av: filename=av-14.2.0-cp313-cp313t-macosx_15_0_arm64.whl size=2121212 sha256=6092004c6b38ce66e9768e2619ba7f92ecb9f5e05820b93cd85b2a4c622823ce
  Stored in directory: /Users/goldbaum/Library/Caches/pip/wheels/89/c9/41/43d93a3a78c72be0683a4a8e10244c74b9ad759e67bc836a81
Successfully built av
Installing collected packages: av
Successfully installed av-14.2.0

No idea if there are deeper issues.