eryksun added the comment: 16.17.2.2 already has a warning after it introduces CDLL, OleDLL, and WinDLL: The Python global interpreter lock is released before calling any function exported by these libraries, and reacquired afterwards. It links to the glossary entry: https://docs.python.org/3/glossary.html#term-global-interpreter-lock It wouldn't hurt to elaborate and box this warning. Subsequently, PyDLL is documented to *not* release the GIL. Also, section 16.17.2.4 documents that CFUNCTYPE and WINFUNCTYPE functions release the GIL and PYFUNCTYPE functions will *not* release the GIL. ---------- nosy: +eryksun _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue18017> _______________________________________