Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ernie.Berkeley.EDU!jas
From: jas@ernie.Berkeley.EDU (Jim Shankland)
Newsgroups: comp.unix.wizards
Subject: SysV IPC:  eyesore or misunderstood art?
Message-ID: <28901@ucbvax.BERKELEY.EDU>
Date: 26 Apr 89 00:49:57 GMT
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: jas@ernie.Berkeley.EDU (Jim Shankland)
Organization: University of California, Berkeley
Lines: 35

In article <13601@ncoast.ORG> allbery@ncoast.UUCP (Brandon S. Allbery) writes:
>AT&T added a new object space (IPC objects) for shared memory, message
>queues, and semaphores.  Presumably they had a reason not to want to use the
>existing object space of file descriptors.  I can imagine the following
>reasoning:
>
>* File descriptors aren't quite general enough to do what we want.
>* Changing fd's to be general (or perhaps flexible) enough will break things.
>* We can design an object space that *is* flexible enough.
>* Once we have done so, we can present them as separate object spaces for SVR2.
>* In future versions, we can start to convert file descriptors into a class
>  of IPC objects... eventually ending up with a single object space again.
>
>[etc.]

Naah.  They just didn't have the imagination to do it right.  The IPC
namespace business is an abomination.  I can't imagine it as a first
step toward a newer, grander vision.  (Of course, that's what they
said about *Dejeuner sur l'herbe*, too.)

Take a look at mmap() in SunOS 4.0 (it didn't actually originate with Sun);
that's a pretty clean way to do shared memory.  And I never have figured
out what message queues give you that you couldn't get by tuning up
pipe semantics a little.

To my mind, the SysV IPC stuff fairly screams:  "glued on to the system
at the last minute as an afterthought."  Your speculation on their line
of reasoning is novel, but even with my most charitable hat on, I just
can't see it.  Anybody who actually helped design this stuff care to
comment?

Jim Shankland
jas@ernie.berkeley.edu

"Blame it on the lies that killed us, blame it on the truth that ran us down"