Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!NUSVM.BITNET!GBOPOLY1
From: GBOPOLY1@NUSVM.BITNET (fclim)
Newsgroups: comp.sys.apollo
Subject: Re: IPC vs SOCKETS
Message-ID: <8905150141.AA08887@umix.cc.umich.edu>
Date: 15 May 89 01:40:50 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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X-Unparsable-Date: Mon, 15 May 89 08:57:56 SST

Hi,
     In article <2005@joshua.athertn.Atherton.COM>, Joshua Levy
(joshua%athertn%pyramid.uucp@lll-lcc.llnl.gov  (Flame Bait)) writes
>I just finished writing some IPC code.  It took me a half day to write
>and a half day to test.  I used neither sockets nor the Apollo stuff,
>but rather UNIX's msgget, msgsnd, msgrcv, and mscgcnt routines.  They
>were exactly what I wanted, and very easy to use.  (I do not use Apollos
>anymore, so I do not know if these routines are part of SR 10.  I'm just
>assuming that since SR 10 is real UNIX, that it includes these routines.
>There is book called "Advanced UNIX Programming" by Marc J. Rochkind
>(Prentice-Hall Software series) which explans how all this works.)
>Joshua Levy

Messages (msg*()), Shared-memory (shm*()), and Semaphores (sem*()) are
part of System V ipc facilities.  These with named pipes (ie FIFO via
mkfifo()) should be bundled with SR10 but users can only use them if
their sys-admin loaded in the System V.

Pipes() may be used for communication between related processes; ie
processes created thro' fork().  Msg*(), shm*(), sem*() and mkfifo()
allows communication between unrelated processes.  However, except for
FIFO, these processes must reside on the same workstation since msgget()
generate a message queue and semget() generate a set of semaphore
variables in the *kernel* and shm*() obviously must share the same memory.
I am not sure about FIFOs.  There is the question of sychroncity between
the producer and consumer processes if they are on different nodes.  Since
the kernel must come in to sychronize these processes, I believe FIFOs
are hard to use in a network.

The book by Maurice Bach, "Design of the Unix Operating System", is a
good place to look into these system calls.

So, we have a sort of hierarchy.  Pipes() may be used only between related
processes.  The other IPC facilities on System V may be used between
unrelated processes in a non-distributed environment.  Finally, BSD socket
may be used in a network.  System V (maybe Release 2 and above) have a
new machanism known as streams.  This works across networks.  I do not
have any info on this except (1) there is an article by Dennis Ritchie
in the July (?) 84 issue of the AT&T Journal -- special issue on UNIX
-- and (2) the Streams Programmer's Guide (?) published by AT&T.

I hope this clears things up.

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