ProcessPoolExecutor code does not get reported

[mikegrima]

Summary

Hello. I am making use of a ProcessPoolExecutor context manager and all code that runs within it is not deemed as covered. I am running this on macOS.

I execute this in tox normally, but this has the same issue outside of tox as well.

The command I run is: pytest --cov --cov-report term-missing tests -n auto. The behavior is the same with or without -n auto for pytest-xdist.

Expected vs actual result

Expected to have the code covered. The actual result is that the code it not seen as covered.

Reproducer

Here is essentially the code that I have:

main.py:

import asyncio
import multiprocessing
from concurrent.futures import ProcessPoolExecutor

async def my_tasker(loop, *args, **kwargs):
    ctx = multiprocessing.get_context("fork")  # my code needs this for a variety of reasons
    with ProcessPoolExecutor(max_workers=10, mp_context=ctx) as executor:
        tasks = []
        for x in range(0, 100):
            tasks.append(loop.run_in_executor(executor, run_in_process, *args, **kwargs))

        results = await asyncio.gather(*tasks)

    return results

def run_in_process(*args, **kwargs):
    # These lines are not seen as covered:
    asdf = 1 + 2
    qwer = 3 + 4
    return "completed"

def main():
    some_args = ["1", "2", "3"]
    loop = asyncio.new_event_loop()
    results = loop.run_until_complete(my_tasker(loop, *some_args))
    loop.close()

    print(results)

    return results

if __name__ == "__main__":
    main()

test_main.py:

from main import main

def test_stuff():
    assert main()

Run pytest --cov --cov-report term-missing -n auto for my tests.

This is the output:

======================================================================================= test session starts ========================================================================================
platform darwin -- Python 3.10.3, pytest-7.2.1, pluggy-1.0.0
rootdir: mycode
plugins: xdist-3.1.0, cov-4.0.0
gw0 [1] / gw1 [1] / gw2 [1] / gw3 [1] / gw4 [1] / gw5 [1] / gw6 [1] / gw7 [1] / gw8 [1] / gw9 [1]
.                                                                                                                                                                                            [100%]

---------- coverage: platform darwin, python 3.10.3-final-0 ----------
Name           Stmts   Miss  Cover   Missing
--------------------------------------------
main.py           24      4    83%   18-20, 33
test_main.py       3      0   100%
--------------------------------------------
TOTAL             27      4    85%

======================================================================================== 1 passed in 0.79s =========================================================================================

Per the output, lines 18-20 are missing, but they are in fact executed.

Versions

Python 3.10.3
pytest==7.2.1
pytest-cov==4.0.0
pytest-xdist==3.1.0

I should hopefully have the code OSS'd soon so that could provide more context, but in the meantime, the code above demonstrates the issue.

[mikegrima]

I did an additional test without the context being set to fork, and it does successfully report the code as covered. It fails when the process is set to fork.

[mikegrima]

I'll also add that I did review this issue but the suggested fix didn't work for me: https://github.com/pytest-dev/pytest-cov/issues/165

[ionelmc]

Yes but that is irrelevant now since multiprocessing support was removed in pytest-cov 4.0. You can try adding this in your coveragerc for the support bultin support from coverage:

[run]
concurrency = multiprocessing
parallel = true
sigterm = true

[mikegrima]

Thanks @ionelmc ! Those changes worked for me. I struggled to find these details though. I mostly reviewed the documentation on this page: https://pytest-cov.readthedocs.io/en/latest/subprocess-support.html. I would be happy to make a PR to add the above details.