Remove EventLoopError::AlreadyRunning

[madsmtm]

This is already prevented by the type-system, and as such it doesn't make sense to have an error case for this.

This was added by @rib in #2767, maybe you can shed some light on if this was an oversight added out of an abundance of caution, or if you think my reasoning is wrong here, and the error actually can happen?

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users

[MarijnS95]

From a quick view this makes sense. The EventLoop cannot be mutably borrowed more than once, and there's no way to Copy/Clone one to get multiple mutable references either.

[rib]

Bit late but I think those checks relate to driving the loop with pump_events.

If you were to initially start running a loop with pump_events and get past dispatching StartCause::Init and set loop_running = true then technically you could then try and use run_on_demand which would now have an un-expected initial state.

Instead of trying to handle that unusual / unexpected mixing of pump_events and run_ondemand these returned an error in that case instead.

[kchibisov]

I don't think that it's an issue actually? Like you can probably start with pump events for one iteration, but then continue with run or run_on_demand?

[kchibisov]

At least it should kind of work now.

[rib]

Like you can probably start with pump events for one iteration, but then continue with run or run_on_demand?

Yeah I think it's just that you'd get ambiguous semantics to try and do something like that, e.g. considering that you probably won't get a StartCause::Init event.

Since it's a weird case, I think my preference at the time was to throw an error instead of having to think about what semantics to promise users.