Cothread generates segmentation faults when run with Coverage

Start by reproducing the crash with tests/test_crash.py using the documented pytest and coverage command under Python 3.11 or newer. Then inspect Cothread's PyThread_* API interactions and compare the failure with the attached Valgrind output. Done means the reproduction completes under coverage without a segmentation fault and related thread interactions are checked for regressions.

In Python3.11+, it seems that Cothread is incompatible with Coverage. Attempting to run it will cause a segmentation fault during Pytest's cleanup stage, presumably at the stage when Coverage is doing its processing.

To recreate, create a Python3.11 virtual environment and add this program to the tests/ directory, named test_crash.py or simiar.

import cothread

def tick():
    print("Test tick print!")

def tock():
    print("Test tock print!")

def test_stuff():
    t = cothread.Timer(0.1, tick)

    cothread.Spawn(tock).Wait()

if __name__ == "__main__":
    test_stuff()

Then run pytest -s --cov=cothread --cov-report term --cov-report xml:cov.xml tests/test_crash.py. You will see something similar to this:

$ pytest -s --cov=cothread --cov-rep
ort term --cov-report xml:cov.xml tests/test_crash.py 
======================== test session starts ========================
platform linux -- Python 3.12.8, pytest-8.3.5, pluggy-1.5.0 -- /scratch/eyh46967/dev/cothread/venv/bin/python3.12
cachedir: .pytest_cache
rootdir: /scratch/eyh46967/dev/cothread
configfile: pyproject.toml
plugins: cov-6.1.1, anyio-4.9.0
collected 1 item                                                    

tests/test_crash.py::test_stuff Test tock print!
PASSEDFatal Python error: Segmentation fault

Thread 0x00007fbf91d02740 (most recent call first):
  <no Python frame>

Thread 0x00007fbf91d02740 (most recent call first):
  File Segmentation fault (core dumped)

A small amount of extra information can be gleaned from running the test under Valgrind: valgrind pytest -s --cov=cothread --cov-report term --cov-report xml:cov.xml tests/test_crash.py. See attached file.

valgrind_output.txt

At this time it is unknown if this is the only incompatibility with Cothread; it is possible other programs that do similar interactions with the various PyThread_* API calls will also suffer from issues or not.