CPython 3.11.11 from uv fails on `multiprocessing.Queue().qsize()` (aarch64)

[gbdjxgp]

Summary

When creating a venv with uv and Python 3.11.11 on linux aarch64, calling multiprocessing.Queue().qsize() raises NotImplementedError. The same code works with uv-managed 3.12.12 and system 3.10.12.

Environment

• OS: Linux (aarch64)
• uv: 0.10.0
• Python (uv-managed):
  • 3.11.11 → NotImplementedError
  • 3.12.12 → works
  • 3.12.14 → works
• Python (system):
  • 3.10.12 → works

Reproduction (sanitized)

user@host:~$ uv venv --python=3.11.11
Using CPython 3.11.11
Creating virtual environment at: .venv
Activate with: source .venv/bin/activate

user@host:~$ source .venv/bin/activate
(venv) user@host:~$ python - <<'PY'
from multiprocessing import Queue
q = Queue()
q.put(1)
q.put(2)
print('uv venv qsize:', q.qsize())
PY
Traceback (most recent call last):
  File "<stdin>", line 5, in <module>
  File "/home/<redacted>/.local/share/uv/python/cpython-3.11.11-linux-aarch64-gnu/lib/python3.11/multiprocessing/queues.py", line 126, in qsize
    return self._maxsize - self._sem._semlock._get_value()
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
NotImplementedError

Expected

qsize() returns 2 (same as 3.12.12 and system 3.10.12).

Comparison

uv Python 3.12.12 (works)

user@host:~$ uv venv --python=3.12
Using CPython 3.12.12
Creating virtual environment at: .venv
Activate with: source .venv/bin/activate

user@host:~$ source .venv/bin/activate
(venv) user@host:~$ python - <<'PY'
from multiprocessing import Queue
q = Queue()
q.put(1)
q.put(2)
print('uv venv qsize:', q.qsize())
PY
uv venv qsize: 2

system Python 3.10.12 (works)

user@host:~$ uv venv --python=3.10
Using CPython 3.10.12 interpreter at: /usr/bin/python3.10
Creating virtual environment at: .venv
Activate with: source .venv/bin/activate

user@host:~$ source .venv/bin/activate
(venv) user@host:~$ python - <<'PY'
from multiprocessing import Queue
q = Queue()
q.put(1)
q.put(2)
print('uv venv qsize:', q.qsize())
PY
uv venv qsize: 2

Notes

This looks specific to the uv-provided CPython 3.11.11 build on aarch64.

[jjhelmus]

I'm not seeing this issue when using the uv provided Python 3.11.14 (the latest patch release).

We do not build older patch releases so any changes going forward will not fix issues in 3.11.11

[jjhelmus]

I believe this change between 3.11.12 and 3.11.13 was a result of using native build for the aarch64 Linux builds in #670

[jjhelmus]

I was able to replicate this issue on a riscv64 machine with the latest patch release:

~$ uname -m
riscv64
~$ uv run --python 3.14 python
Python 3.14.3 (main, Feb  3 2026, 22:43:04) [GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from multiprocessing import Queue
... q = Queue()
... q.put(1)
... q.put(2)
... print('uv venv qsize:', q.qsize())
...
Traceback (most recent call last):
  File "<python-input-0>", line 5, in <module>
    print('uv venv qsize:', q.qsize())
                            ~~~~~~~^^
  File "/home/jhelmus/.local/share/uv/python/cpython-3.14.3-linux-riscv64gc-gnu/lib/python3.14/multiprocessing/queues.py", line 124, in qsize
    return self._maxsize - self._sem.get_value()
                           ~~~~~~~~~~~~~~~~~~~^^
  File "/home/jhelmus/.local/share/uv/python/cpython-3.14.3-linux-riscv64gc-gnu/lib/python3.14/multiprocessing/synchronize.py", line 143, in get_value
    return self._semlock._get_value()
           ~~~~~~~~~~~~~~~~~~~~~~~~^^
NotImplementedError