The following resources have useful information on messaging and RPC:
EventServer, available on CPAN, provides a replacement for Msg's event_loop procedure and supports callbacks for file and time-out events.
Unix Network Programming. W. Richard Stevens. Prentice-Hall, 1990.
Advanced Programming in the Unix Environment. W. Richard Stevens. Prentice-Hall, 1992.
"A Note on Distributed Computing." Jim Waldo, Geoff Wyant, Ann Wollrath, and Sam Kendall. Available at http://www.sunlabs.com/techrep/1994/abstract-29.html (Technical Report TR-94-29).
A very well-written report on the problems associated with RPC (the concept) and distributed computing in general. (In fact, other technical reports at SUN's research labs also make for good reading.)