> Using a full-featured RPC framework for IPC seems like overkill when the processes run on the same machine.

That is exactly what COM/WinRT, XPC, Android Binder, D-BUS are.

Naturally they have several optimisations for local execution.

What I loved about Fuchsia was its IPC interface, using FIDL which is like a more optimized version of protobufs.

https://fuchsia.dev/fuchsia-src/get-started/learn/fidl/fidl

Had to reach for a new IPC mechanism recently to implement a multi-GPU LLM inference server.

My original implementation just pinned one GPU to its own thread then used message passing between them in the same process but Nvidia's NCCL library hates this for reasons I haven't fully figured out yet.

I considered gRPC for IPC since I was already using it for the server's API but dismissed it because it was an order of magnitude slower and I didn't want to drag async into the child PIDs.

Serializing the tensors between processes and using the Servo team's ipc-channel crate[0] has worked surprisingly well. If you're using Rust and need a drop-in (ish) replacement for the standard library's channels, give it a shot.

[0] https://github.com/servo/ipc-channel

At a project I worked at we were considering using protobuf for IPC between our desktop app and our network framework code which used different languages.

The performance was part of the reason (compared to serializing using JSON) but the main reason was just tooling support for automatic type checking. gRPC can generate types from a schema for all popular languages out there.

We ended up taking another route but I feel it is important to consider the existing tools ahead of any performance concerns for most cases

> Using a full-featured RPC framework for IPC seems like overkill when the processes run on the same machine. However, if your project anyway exposes RPCs for public APIs or would benefit from a schema-based serialisation layer it makes sense to use only one tool that combines these—also for IPC.

It might make sense. Usually, if you're using IPC, you need it to be as fast as possible and there are several solutions that are much faster.