Optimize Local Message Passing

[stuartmscott]

Messages send to self, or to other State Machines on the same host could avoid going through the networking stack and therefore gain a performance improvement.

Split out from #11

[winksaville]

Connection features:

• Sending is always non-blocking
• Sending should take roughly constant time
• Sending does not mean message will be received
• Lossless except on disconnect
• Notify sender & receiver on disconnect
• Ordered between a sender / receiver pair.

Related features:

• Actors can choose to share a thread with other actors if they guarantee they don't block.
• Actors can choose to not share a thread.

For connections with in a process and potentially between processes the above features are possible using a queue based on linked lists although there needs to be space for link(s) in the message.

In addition, an instance of this connection should be usable as a front and back end for a connection across an appropriate network protocol.

Multiple Producer Single Consumer or MP Multiple Consumer (MPSC or MPMC) linked list queues are a solution.

Rust crossbeam_channel is a start:
https://docs.rs/crossbeam-channel/latest/crossbeam_channel/

C++:
https://www.google.com/search?q=c%2B%2B+unbounded+mpsc+or+mpmc+queue