UNIX IPC

[Norman Azadian]

The author of the reference article suggested building a low-performance
IPC using unix signal/kill routines.  I thought the same thing many months
ago and decided to build it for a project.

My design had a "message switch" process which started up all the application
processes with two pipes to each.  There was a library of IPC routines that
the application processes could use to make sending and receiving messages
easy and straightforward.  In one mode of operation, the "message switch"
process spent all it's time looking for messages on it's input pipes
(this is a star system) and routing them to the appropriate output pipes.
The application processes had to poll their receive pipe similarly.
More sophisticated versions involved signals to and from the "message switch".

The signalling scheme worked well at low speeds, but started to fall apart
as the message traffic increased.  Signals seemed to just get lost in space.
This was with a vax-11/780 running 4.1bsd.  I still have the code if anybody
is interested.  I believe the strictly-polling mode works.

					NHA