What's the message passing IPC with the least RTT for messages that are in the 16-32 byte range? It's gonna run approximately once per command in an interpreter.

The answer is: 42
Now you need to figure out the question.

Assuming local: shared mmap locked by futex, use it as a stack, add a unix domain socket but only for passing the path to the file-backed memory from one end to the other.

Else TCP, like a fucking square.

@Liebranca stdio is 20μs so I'm starting with that just to have a poc of the rest of the system because it's really simple and inherently cross-platform, but I'm also researching this now to make choices that will work well with it. Thanks!

@Liebranca TCP takes a very impractical approach to guaranteed delivery that makes things unnecessarily slow in response to any amount of packet loss, even a very generic UDP-based protocol can do better. I'd only ever pick TCP for a MVP and I'd make sure to define an abstract packet-based interface.

@lorentz It's a "reliability" overhead ;>

But supposing that pains in the ass like congestion are not a concern then you can obviously do a lot better; much of that overhead is redundant in a controlled environment.