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From: tpm@datlog.co.uk ( Tim Murnaghan )
Newsgroups: comp.unix.wizards
Subject: Re: A very interesting problem -- multiprocessing
Message-ID: <690@dlvax1.datlog.co.uk>
Date: Wed, 6-May-87 12:17:27 EDT
Article-I.D.: dlvax1.690
Posted: Wed May  6 12:17:27 1987
Date-Received: Sat, 9-May-87 09:43:15 EDT
References: <7176@brl-adm.ARPA> <4589@sci.UUCP> <2017@utah-gr.UUCP>
Reply-To: tpm@datlog.co.uk ( Tim Murnaghan )
Organization: Data Logic Ltd, Queens House, Greenhill Way, Harrow, London.
Lines: 26

In article <2017@utah-gr.UUCP> thomas%spline.UUCP@utah-gr.UUCP (Spencer W. Thomas) writes:
>
>
>Anyway, if you want to coroutine a couple of functions with no
>arguments (easiest case), you just allocate a "large enough" chunk of
>memory for each one's stack, set the stack pointer to the correct end
>of it (top on a Vax), and call the function.  (Oh, I should mention
>that you need to save the real stack pointer somewhere.)  The
>"Suspend" action then saves the co-routine stack pointer in a static
>variable, and resumes execution on the real stack.  To continue a
>co-routine, you restore its saved stack pointer and do a subroutine
>return.  Maybe a little code fragment would help:
>....
Of course you don't have to use assembler to do the stack setting, setjmp
remembers everything that you need.
All you have to do is gallop down the stack until you've left enough stack
for the coroutine below and then do your setjmp (we have a routine called
gobble).
Some implementors have qualms about longjmp'ing the wrong way which is a shame,
but at least the asssembler bits can be hidden behind a standard interface
when you write your own.

We do actually use this sort of thing (with a bit more business for
synchronisation ) keeping our co-routines on a list and having a noddy
scheduler kick them off and calling them activities (for we are using the MOD
methodology MASCOT).