Enable free threading support - #255
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August 11, 2026 15:47
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| # Oversubscription: MKL spawns its own thread pool per calling thread, so | ||
| # running MKL VM calls from many Python threads concurrently can spawn | ||
| # far more OS threads than cores. Cap it before mkl_umath/MKL initialize. | ||
| os.environ.setdefault("MKL_NUM_THREADS", "1") |
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Can you verify that this actually works, and that the MKL thread count is actually capped? It's not clear to me that MKL won't be initialized already in some environments, either, especially ones with mkl-service, etc.
I think it would be best to avoid trying to set environment variables this way if possible, too, as it can be unreliable, but as long as we verify it should be ok
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Adds free-threaded (GIL-disabled) CPython 3.14t support to
mkl_umathby declaring both the Cython extension and the hand-written_ufuncsC extension as free-threading compatible, aligning build tooling requirements, and expanding CI/conda packaging to cover both CPython 3.14 (GIL) and 3.14t (free-threaded) variants.Changes:
mkl_umath/src/_patch_numpy.pyxasfreethreading_compatiblefor Cython, and declarePy_MOD_GIL_NOT_USEDin the_ufuncsC extension (ufuncsmodule.c) so importing either module no longer re-enables the GIL.>=3.1.0across build/packaging (pyproject.toml, both conda recipes,AGENTS.md,README.md).cython >=3.1.0and removepython-gilpins.cp314andcp314tvariants and adjust cache/artifact naming accordingly.