SANIC_NO_UVLOOP=true doesn't seem to work

[delfick]

Describe the bug
Installing sanic with a SANIC_NO_UVLOOP=true in my environment still results in uvloop being installed

Environment (please complete the following information):

• OS: macOS Big Sur
• Version 11.5.2

Additional context
Python 3.9.6

[ahopkins]

If you look at the unit tests, you can see if definitely works. Perhaps you have pip cache?

[delfick]

--no-cache-dir doesn't make a difference and also given it's decided in sanic's setup.py based on the environment variable, it wouldn't make sense for it to anyway!

After some checking, I think the reason is because the wheel doesn't have a setup.py and so when you install via a wheel it doesn't ever do this check https://github.com/sanic-org/sanic/blob/main/setup.py#L138

[ahopkins]

One of the things that has been a question for a long time on this project is how to gracefully handle this. Obviously, the best scenario would be if pip supported subtractive install_requires:

$ pip install sanic[no-uvloop]

This (to my knowledge) is still not a supported feature. The problem is that we do want uvloop to be installed by default. That will not change. The only other solution that would work is if you do this:

pip install sanic
pip uninstall uvloop

Not ideal, but in CI it is not terrible.

If you have some other thoughts or suggestions, please let me know.

[delfick]

can we make it so that sanic chooses to use it at runtime rather than forced on us at import time? i.e. I can set an environment variable or sanic option that makes it not set uvloop? that way uvloop can be in the environment, but sanic can choose to not use it

[delfick]

i.e. move

sanic/sanic/server.py

Line 51 in b1b12e0

asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

to when you use the loop or make this not happen depending on an environment variable.

[ahopkins]

can we make it so that sanic chooses to use it at runtime rather than forced on us at import time? i.e. I can set an environment variable or sanic option that makes it not set uvloop? that way uvloop can be in the environment, but sanic can choose to not use it

Yeah, that can probably work fine. I did something similar with uvloop by allowing for an application override (for dumps only, we still need to add it for loads).

Probably app.config.NO_UVLOOP would be the most appropriate/consistent, but open to seeing whatever you come up with in your PR.

[delfick]

Awesome! Thank you so much :)

[prryplatypus]

Hope it works! :)

[delfick]

Thanks ❤️