coverage.py isn't showing the expected results for celery prefork model

[BPraveenRaja]

Describe the bug coverage.py isn't working for the processes that are not spawned, celery uses prefork model to create processes

To Reproduce How can we reproduce the problem? Please be specific. Don't link to a failing CI job. Answer the questions below:

1. What version of Python are you using? Python3.9
2. What version of coverage.py shows the problem? The output of coverage debug sys is helpful. the latest version
3. What versions of what packages do you have installed? The output of pip freeze is helpful. amqp==5.1.1 billiard==4.1.0 blinker==1.6.2 celery==5.3.1 click==8.1.7 click-didyoumean==0.3.0 click-plugins==1.1.1 click-repl==0.3.0 coverage==7.3.0 Flask==2.3.3 itsdangerous==2.1.2 Jinja2==3.1.2 kombu==5.3.1 MarkupSafe==2.1.3 prompt-toolkit==3.0.39 python-dateutil==2.8.2 redis==5.0.0 six==1.16.0 tzdata==2023.3 vine==5.0.0 wcwidth==0.2.6 Werkzeug==2.3.7
4. What code shows the problem? Give us a specific commit of a specific repo that we can check out. If you've already worked around the problem, please provide a commit before that fix. Explained the problem in the next message.
5. What commands should we run to reproduce the problem? Be specific. Include everything, even git clone, pip install, and so on. Explain like we're five! Explained the problem in the next message.

Expected behavior A clear and concise description of what you expected to happen.

Additional context Add any other context about the problem here.

[nedbat]

Hi, can you provide us with code to run to demonstrate the problem? It's hard to debug your situation without it.

[BPraveenRaja]

Hi, I'm sorry for the late reply. I lost track of this issue.

Here is the link to the code repo url

This application uses flask and celery. This application generally creates a file using celery, and it uses Flask web framework

Please note I'm using sitecustomize.py and COVERAGE_PROCESS_START environment variable to start the coverage process.

Scenario 1: When I ran the celery with pool solo | threads In one terminal, I ran python run.py and in another terminal, I ran celery -A celery_worker.celeryInstance worker --loglevel=debug --pool=solo

I executed a few cases in the browser, I have hit the URL in the browser to create a file using Flask and celery The coverage report is perfectly shown below

Scenario 2: When I ran the celery with pool prefork(default) In one terminal, I ran python run.py and in another terminal, I ran celery -A celery_worker.celeryInstance worker --loglevel=debug --pool=prefork

I executed the same cases as scenario 1 in the browser, I hit the URL in the browser to create a file using Flask and Celery The coverage report is wrongly shown below