deprecate NIOEventLoopGroupProvider.createNew

[weissi]

Motivation:

NIOEventLoopGroupProvider.createNew was probably never a good idea because it creates shutdown issues for any library that uses it. Given that we now have singleton (#2471) EventLoopGroups, we can solve this issue by just not having event loop group providers.

Users can just use group: any EventLoopGroup and optionally group: any EventLoopGroup = MultiThreadedEventLoopGroup.singleton.

Modifications:

• deprecate NIOEventLoopGroupProvider.createNew
• soft-deprecate (document as deprecated but don't mark @available(deprecated)) NIOEventLoopGroupProvider

Result:

• Libraries becomes easier to write and maintain.
• Fixes ecosystem issue: EventLoopGroupProvider and the 'similar create or share ELG' pattern #2142

[weissi]

Must be merged after #2471

[adam-fowler]

group: any EventLoopGroup = MultiThreadedEventLoopGroup.singleton is not a great alternative as it is no use if NIOPosix is not available. Also it would be good if apple/swift-nio-transport-services#180 was also merged before this got merged.

Any library that supports both Posix and Network framework will probably end up having to implement a new version of NIOEventLoopGroupProvider which replaces createNew with useSingleton or something similar. It might be better if this type came from NIO though to provide consistency.

[weissi]

group: any EventLoopGroup = MultiThreadedEventLoopGroup.singleton is not a great alternative as it is no use if NIOPosix is not available.

That's a good point.

Also it would be good if apple/swift-nio-transport-services#180 was also merged before this got merged.

Yes, I'll work on that rn.

Any library that supports both Posix and Network framework will probably end up having to implement a new version of NIOEventLoopGroupProvider which replaces createNew with useSingleton or something similar. It might be better if this type came from NIO though to provide consistency.

I'd hope that libraries could use eventLoopGroup: any EventLoopGroup? = nil where nil means "default" and what that means can be chosen by the library itself. That way we also don't leak the exact value into the API. WDYT?

[adam-fowler]

I'd hope that libraries could use eventLoopGroup: any EventLoopGroup? = nil where nil means "default" and what that means can be chosen by the library itself. That way we also don't leak the exact value into the API. WDYT?

That'd work I guess

[1proprogrammerchant]

I'd hope that libraries could use eventLoopGroup: any EventLoopGroup? = nil where nil means "default" and what that means can be chosen by the library itself. That way we also don't leak the exact value into the API. WDYT?

That'd work I guess

give it a try

[weissi]

friendly ping @Lukasa

[weissi]

@Lukasa / @glbrntt addressed, ptal