Add --timeout-graceful-shutdown parameter

[Kludex]

• Closes How do I cancel a streaming response on shutdown? #451
• Closes Make force_exit configure-able from command line #675

Description

This PR adds the --timeout-graceful-shutdown parameter, which sets a timeout on tasks that the server is waiting to perform the shutdown lifespan event.

This timeout doesn't act on the shutdown lifespan event i.e. the shutdown event is supposed to run even in the scenario the tasks are timed out.

I need to think of a nice test for this. Ideas?

Notes

1. The --graceful-timeout from gunicorn is conceptually different from --timeout-graceful-shutdown. The first forcefully kills the worker, and the latter cancels the tasks that are running after uvicorn said "I'm not receiving more requests, I'm just going to finish some tasks".

2. An alternative name for this parameter could be --timeout-tasks-shutdown, or similar.

3. The logs are horrible when a task is cancelled. Should it be fine tho? 🤷

Missing

• Add an entry on the documentation, and mention the difference with --graceful-timeout from gunicorn.
• Add a test case.

[JonasKs]

Reminds me of python-arq/arq#345 😁 I'd love to see this merged.
As for a test, I agree, not an obvious pretty comes to mind.
I think I would've went for caplog test on this one personally.

[Kludex]

The problem on this PR is that run_asgi task gets cancelled, and there's a horrible asyncio.CancelledError message.

Also, I guess we need to cancel the tasks (?) in case TimeoutError happens. 🤔

[Kludex]

• Close in favor of Add --timeout-graceful-shutdown parameter #1950