I would like a super lightweight host process for interpreters that is similar to php-fpm and Erlang but can have shared state for database connections but the main interpreter is not a separate process but simply a function call.

Serverless and WASM runtimes are similar and Firecracker are in this space.

It would have to be multithreaded, it could communicate with nginx via domain socket as php-fpm does. I don't know if there's a way to multiplex data over a domain socket, maybe you could use multiple domain sockets and load balance between them? Or custom framing.

Does head of line blocking come into this too?