[python] Cleanup ThreadPool with atexit rather than __del__

[fabianvf]

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Description of the PR

This removes the __del__ function from the generated Python client,
and replaces it with a cleanup function. When a ThreadPool is created,
the cleanup function is registered with the atexit module.

This fixes #9991, where the API client could hang indefinitely at
garbage collection.

cc @kenjones-cisco

[fabianvf]

@gaborbernat that might be the fastest review I've ever gotten, got it in while I was writing up the PR description. I think I addressed your comments

[gaborbernat]

I feel like maybe instead cleanup should be close and we should now also allow to call the client with the with statement, so it may cleanup automatically whenever the user no longer needs it.

[fabianvf]

@gaborbernat renamed cleanup to close, think making it a context manager might be a bit out of scope for this bugfix but I can make a followup PR for it

[anichari]

Hello, has this been merged and available in the latest codegen packages? I tried a few things with codegen versions but I still dont see this change in the api_client.py generated files.

1. I used 2.0.14-SNAPSHOT (built from master) and with that code, I still see the lazy init of ThreadPool rather than the newer code that creates the ThreadPool in init.
2. I used 3.0.19 (brew installed) and with that, the del method is still there, no sign of above changes to api_client.py in that either.

[gaborbernat]

Nope, we've moved on to use OpenAPITools/openapi-generator#5094 instead, that contains the fix. Swagger never addressed this issue.

[anichari]

Nope, we've moved on to use OpenAPITools/openapi-generator#5094 instead, that contains the fix. Swagger never addressed this issue.

Thx much