IPC facilities (shared memory)

[Andy Valencia]

	We used it to connect together the two parts of our SNA
product.  The "nucleus" part, which handles the SDLC link, always
runs.  When you want an SNA terminal (327x type), you run the
"PS (Presentation Service)".  It talks over System-V messages.
But because message IDs aren't file descriptors (thanks, AT&T),
and because we don't get select() in any case, you always have to
follow a message write with a signal, when writing from Nuc. to PS
(because PS blocks on keyboard), and you don't send one PS to Nuc.,
because the Nuc. blocks on the message port--the SDLC driver signals
when it gets something.

	In case you haven't gathered it from the above, it takes
a reasonable amount of dancing about to get "real life" products
running with it.  I imagine that having multiple threads of
execution will mitigate this, as you can then just block a thread
on each resource.

				Andy Valencia
				vandys%hpindda.UUCP at hplabs.hp.com