Deprecate app.on_loop_available signal

[asvetlov]

From my understanding on app.on_startup the loop is already present.
Why do we need additional signal?
app.on_loop_available is not documented BTW
@fafhrd91 ?

[fafhrd91]

I think this was for config and runtime separation. I am not sure if it is useful, we can deprecate any of those.

[kxepal]

+1 to deprecate and remove on_loop_available, don't see how it could be useful.

[justanr]

It looks like on_loop_available happens outside running the event loop, right? That's useful for doing blocking setup or interacting with third party packages that use the various run methods on the loop to do work. I've run into an issue where a package tries to use the loop to do something but it's already running so it just crashes.

[asvetlov]

It looks like on_loop_available happens outside running the event loop, right?

No, there is no such guarantee.

If you need to do something blocking etc -- please do it before run_app() call.

[justanr]

Ah, in that case, yeah it should probably go the way of the dodo.

[lock]

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