Bug report

Bug description:

I got a bug report on python-zlib-ng where using the threaded opening the program would hang if an exception occurred and a context manager was not used.

I fixed it by changing the threads to be daemonic: pycompression/python-zlib-ng#54.

This fixes the issue on python 3.9, 3.10, 3.11 and 3.12, but not 3.13-rc2. Also the latest main branch is affected. Unfortunately I could not create a minimal reproducer, other than running the test directly. Daemonic threads seem not to work in this particular case, where there are some BufferedIO streams and queues involved.

git clone -b issue53 https://github.com/pycompression/python-zlib-ng
# Build Cpython
./python -m ensurepip
./python -m pip install pytest pytest-timeout <path to python-zlib-ng repo>
./python -m pytest <path to python-zlib-ng repo>/tests/test_gzip_ng_threaded.py::test_threaded_program_can_exit_on_error

Since there are many code changes between 3.12 in 3.13 the underlying cause is surely there, but it is hard to pinpoint.

CPython versions tested on:

3.13, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-123940: Ensure force-terminated daemon threads can be joined #124150