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From: libes@nbs-amrf.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: A very interesting problem -- multiprocessing
Message-ID: <514@nbs-amrf.UUCP>
Date: Wed, 6-May-87 02:30:37 EDT
Article-I.D.: nbs-amrf.514
Posted: Wed May  6 02:30:37 1987
Date-Received: Wed, 13-May-87 07:07:52 EDT
References: <7176@brl-adm.ARPA> <4589@sci.UUCP> <2017@utah-gr.UUCP>
Organization: National Bureau of Standards, Gaithersburg, MD
Lines: 40
Summary: XINU provides multitasking in a single process

Comer's XINU provides multitasking in a single process.  If your
coroutines explicitly give up control, you can use setjmp/longjmp.
If you want preemptive scheduling, you must save the registers by
hand with a little assembler, and set up a timer interrupt that
calls the scheduler.

I ported XINU to a 68k running 4.2 and it works great.  Here is
your program rewritten in XINU:

void proc1()
{
	for (;;) fprintf(stderr,"1");
}

void proc2()
{
	for (;;) fprintf(stderr,"2");
}

user_main()
{
	xresume(xcreate(proc1,2000,20,"proc1",0));
	xresume(xcreate(proc2,2000,20,"proc2",0));
}

The args to xcreate (X for Xinu to avoid conflicts with UNIX funcs)
are 1) function, 2) stack size (I use 2000 because fprintf uses a
lot!), 3) priority, 4) function name, 5) number of arguments to
function, 6) optional arguments.  Currently, the quantum size is
compiled into the scheduler, but that could also be passed as an
argument.

I wrote this all up in a paper, and submitted it to USENIX but it
was rejected.  Now it's being studied by the ;login:  folks.  If
they don't like it, perhaps I'll just give up and have it printed
locally as a TR.  I know it's not much, but so many people have
expressed interest in it, I figure it must be worth printing
somewhere.  Any suggestions?

Don Libes                {seismo,mimsy}!nbs-amrf!libes