Bug report

On Windows, thePy_GIL_DISABLED macro is not defined when building C API extensions with the free-threaded build of CPython 3.13 (i.e.,--disable-gil). Now that biased reference counting (6dfb8fe) landed, this leads to incorrect/failed compilation of extensions on Windows¹. The problem does not occur on Linux/macOS and other./configure based builds because that build system defines thePy_NOGIL macro as part ofpyconfig.h. On Windows,Py_GIL_DISABLED instead defined as a pre-processor definition inpyproject.props, but that's used by C-API extensions.

Among other problems, this leads totest_peg_generator failing on the nogil Windows buildbot (example failure).

I can think of two possible approaches to fixing this:

1. Modify setuptools (maybe setuptools.distutils?) to definePy_GIL_DISABLED when invoking the compiler ifsysconfig.get_config_var("Py_NOGIL") isTrue.
2. In the CPython Windows build, generate a header file defining/undefingPy_GIL_DISABLED depending on if the build is invoked with--disable-gil or not.

The first option seems a little more straightforward to me, but there is a risk that we might encounter this same issue across multiple extension build systems. The second option seems like it would more robustly address this issue.

Linked PRs

• gh-111650: Generate pyconfig.h on Windows #112179
• gh-111650: Ensure pyconfig.h includes Py_GIL_DISABLED on Windows #112778