Free Threaded Python Dependency Compatibility

[cburroughs]

To use Free Threaded Python with no GIL every C abi dependency needs to support that https://docs.python.org/3/howto/free-threading-python.html#the-global-interpreter-lock-in-free-threaded-python.

We need to:

• Upgrade every dep to a version that supports with a free threaded version available.
• Select (TBD how? Is there a regular marker ) the free threaded (t) version

user_reqs.lock deps using C abi:

• cryptography
• psutil
• pynacl

[cburroughs]

Actually using Free Threading obviously also needs #22769

[jsirois]

I'll note messing this up nets a quick SIGSEGV on import of the native code linked against a non-free-threading Python build. This is what I saw over testing science running Python 3.14 free threaded with a non-free-threaded psutil wheel:

(gdb) bt
#0  __strcmp_evex () at ../sysdeps/x86_64/multiarch/strcmp-evex.S:1571
#1  0x0000000001c653af in _PyImport_ResolveNameWithPackageContext (name=0xffffffffffffffff "") at Python/import.c:754
#2  _PyModule_CreateInitialized (module=0x743ce98353a0 <moduledef>, module_api_version=<optimized out>) at Objects/moduleobject.c:228
#3  0x0000000001cd90ca in ?? ()
#4  0x0000743ce9831923 in PyInit__psutil_linux () at psutil/_psutil_linux.c:68
#5  0x00000000019bfe38 in _PyImport_RunModInitFunc (p0=0xffffffffffffffff, info=0x318e5bd63a0, p_res=0x0) at ./Python/importdl.c:429
#6  0x00000000019bfd82 in import_run_extension (tstate=0x16f7d30 <_PyRuntime+310448>, p0=0x743ce9831910 <PyInit__psutil_linux>, info=0x7ffce77c2b28, spec=0x318e473e9d0, 
    modules=<optimized out>) at Python/import.c:1996
...

[jsirois]

Select (TBD how? Is there a regular marker ) the free threaded (t) version

There is no marker yet; see links below for some of the typical sordid history of PyPA inaction. You select by building your PEX with a free-threaded CPython in the 1st place (either by running the Pex CLI with it or via --python), or by using a complete platform generated from one of these. In short, you select via interpreter compatibility tags currently and that's the only way.

• https://discuss.python.org/t/environment-marker-for-free-threading/60007
• https://discuss.python.org/t/pep-780-abi-features-as-environment-markers/86013/31

[cburroughs]

oh, wow. Thank you for the pointers regarding selection.