Thread-safety of maxminddb C extension with Python free-threaded (no-GIL) build

[otsuka]

Hi team,

When importing maxminddb on Python’s experimental free-threaded build, I see a warning stating that the GIL has been enabled because the module hasn’t declared that it can run safely without the GIL.

Is the maxminddb C extension actually safe to use in a multi-threaded context when the interpreter is running without the GIL?

% python
Python 3.13.7 experimental free-threading build (main, Aug 30 2025, 00:32:10) [Clang 17.0.0 (clang-1700.0.13.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import maxminddb
<frozen importlib._bootstrap>:488: RuntimeWarning: The global interpreter lock (GIL) has been enabled to load module 
'maxminddb.extension', 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.

Thanks!

[horgh]

I believe that message is accurate and it is not currently safe. We are planning to investigate whether we can do this, but we haven't done it yet.

[horgh]

After talking with my colleague, the extension might be okay thread safety wise after all. However we haven't looked into it in depth yet. If you wanted to experiment with it, you could try setting the environment variable PYTHON_GIL=0 like the warning mentions.