NIO client: ClientBootstrap.channelInitializer can be called multiple times

[weissi]

This is just something to watch out for. In NIO 1&2, the channelInitializer can be called multiple times because we do happy eyeballs with real channels. So you might see one being brought up for IPv4 and one for IPv6. NIO will close the losing one, so as you'd expect only one channel will survive (and be handed to you via connect's future) however there might be multiple channelInitializers run.

The code right in here assumes that this doesn't happen. So worst case (unlikely) is that the Channel that NIO decides to kill will complete the multiplexerPromise and then you're left in a bad spot: multiplexerPromise succeeded with the multiplexer from the closed Channel. Likely outcome for this situation would be random hangs. In this NIO issue I describe how to handle this situation and that we should in the future offer something easier than what you have to do today.

[MrMage]

The code right in here assumes that this doesn't happen. So worst case (unlikely) is that the Channel that NIO decides to kill will complete the multiplexerPromise and then you're left in a bad spot: multiplexerPromise succeeded with the multiplexer from the closed Channel.

Could that be what is actually happening in #430?

[glbrntt]

Quite possibly; I came across this the other day but haven't pushed up the fix yet.

[MrMage]

Fixed by #439.