Preferred portable way to talk to a server process

Hello,

what's the preferred, portable way in NSPR to talk to a server process
for saying such things as "do a clean shutdown", "reload your config
file", "re-index your database" and so on?

I've read that (Unix-)signals are highly non-portable. Which
interprocess communication concept should I
use to get the same code running under Unix and Windows?

BTW, is there an equivalent for getpid() in NSPR?

BTW2: I miss a full-text search through the documentation for looking up
keywords such as "getpid", "signal" etc.

Greetings,
Joachim