Consider adding EventLoopGroupProvider.eventLoopGroup and EventLoopGroupProvider.syncShutDownIfNotShared

[MrLotU]

In NIO 2.21.0 a new enum EventLoopGroupProvider was introduced for easy passing around of EventLoopGroups in third party libraries.

This has been a great tool in lots of places, but still leaves the following code in nearly all client-libraries:

let eventLoopGroup: EventLoopGroup

switch eventLoopGroupProvider {
case .shared(let elg): eventLoopGroup = elg
case .createNew: eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount)
}

or something very similar. And along with this "setup" code almost all these blocks also come with a similar switch statement to shut down the ELG when .createNew or pass over when .shared()

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I would like to propose one new method and one new property to be added to EventLoopGroupProvider.
First off EventLoopGroupProvider.eventLoopGroup that would return the EventLoopGroup in a one-liner, using the above switch statement internally.

Second off EventLoopGroupProvider.syncShutDownIfNotShared to shut down the ELG in case it's been newly created.

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Curious to hear your input on if this has a place within NIO, or should stay in third-party libraries. Thanks!

[Lukasa]

I think the computed property seems sensible, and we should definitely add that. I am less confident about adding the createNew stanza: it excessively privileges MultiThreadedEventLoopGroup, which is not necessarily a good default in some platform situations. For now I think leaving that out, but adding the shutdown computed property seems sensible to me.

[MrLotU]

Thanks! I will open up a PR :)

[weissi]

EventLoopGroupProvider was a mistake (see #2142 & #2480), I think we can close this.