Support freethreading Python #16

Activity

1. hroncok commented on Nov 3, 2025

   

   hroncok

   on Nov 3, 2025

   MemberAuthor

   More actions

   I talked about this with @encukou. Assuming the crypt_r call itself is thread safe¹, the only potentially problematic part of the code is Py_TYPE(args[1])->tp_name:

   crypt_r/src/_crypt_r.c

   Lines 37 to 40 in a52c167

   	PyErr_Format(
   	PyExc_TypeError, "crypt argument 1 (word) must be string, not %s",
   	Py_TYPE(args[0])->tp_name
   	);

   1. an argument is passed of type X
   2. we call Py_TYPE on it, and get X which does not increment the refcount
   3. the type of the argument is changed by another thread (e.g. by assigning to __class__)
   4. all other instances of this type are gone, garbage collected, the type is deallocated
   5. we call ->tp_name on garbage

   This is technically almost impossible to happen but it might :D

   A solution is to use the %T format here instead, which likely has the same problem, but the implementation is in Python and is no longer "our problem". %T was added in Python 3.13.

   Footnotes

   1. Where the r stands for re-entrant, so we assume it is. ↩
2. hroncok

   added a commit that references this issue on Nov 24, 2025

   On Python 3.13.0a6+, use the %T format in exception messages

   ...

   9b8d763