Idea sketch / concept art: Round Robin Balancing

[blakesmith]

This is untested "concept art" to demonstrate some of the ideas of how we might add round-robin publishing to the client. There are definitely concurrency things to work out (misuse of atomics), as well as some potentially slow paths along the publishing path like using streams.

This is meant more just to get some core ideas across, that we can refine and iterate on together:

• I think a lot of the complexity of the existing mainline publisher is due to connection failures being tracked at the completely wrong level (on the Publisher directly). My draft attempts to move connection failure state down to the connection itself.
• I played around with a PublisherConnectionPool abstraction to manage handing out connections.
• Relocating these concerns enabled keeping the PublisherBalanceStrategy interface really slim: Just one method that hands out connections from the pool.