> You don't need a "full protocol parser" for sockets either. You can send/receive C structs just fine. It's also not hard to write to sockets from the command line.

Yeah, that's how you get vulnerabilities. For the same reason that "Thou shalt not write async signal handlers without extreme care", thou must never send data down a socket without a clear specification for communication. It doesn't (and shouldn't) have to be a "complicated" protocol. But it absolutely must be a fully specified one.

And signals, as mentioned, don't really have that shortcoming due to their extreme simplicity. They're just interrupts and don't pass data (except in the sense that they cause the target to re-inspect state, etc...). They're a tool in the box and you should know how they work.

Mostly the point is just "IPC is hard", and choosing tools isn't really the hard part. Signals have their place.