Path: utzoo!attcan!uunet!husc6!mailrus!ames!pasteur!ucbvax!UIAMVS.BITNET!AWCTTYPA
From: AWCTTYPA@UIAMVS.BITNET ("David A. Lyons")
Newsgroups: comp.sys.apple
Subject: Multitasking GS?
Message-ID: <8806131207.aa23114@SMOKE.BRL.ARPA>
Date: 14 Jun 88 12:53:21 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 39
X-Unparsable-Date: Friday 10 Jun 88 10:34 PM CT

>Date:         Thu, 9 Jun 88 01:11:25 GMT
>Reply-To:     Info-Apple@BRL.ARPA
>From:         Doug Gwyn <gwyn@brl-smoke.arpa>
>Subject:      Re: Multitasking GS?

>It isn't really practical to use the SOFTSWITCH technique with 16-bit
>programs.  However, with the memory manager and loader that the GS
>has, most of the basic hooks are present for reasonable multitasking.
>The hard part is getting tasks to relinquish the processor so that
>others have a chance to run.

It's not really that big of a problem--you could do it like
MultiFinder does on the Macintosh, through GetNextEvent calls
(sometimes calling GetNextEvent gives another application control for
a while).  You'd also want to patch some Menu Manager functions to
allow clicking at the right end of the menu bar to cycle to the next
application.  Some applications will be less standard & won't call
the menu manager or maybe not even the event manager--that's OK; you
can still install a routine that hooks into the keyboard
microcontroller hooks and detects certain keypresses (I think).

>SOFTSWITCH relies on the control-panel interrupt for manual context
>switching; a 16-bit version would leave all the program memory in
>place and save just the display memory and a little bit of stack.

Actually it wouldn't be *necessary* to save the display, at least
not for applications that use the window/menu managers, since those
applications can reconstruct the display if the system asks them to
(try RefreshDesktop(nil) ).  If the display gets rebuilt after you
use the Meltdown NDA (by Jason Harper), the multitasker could do the
same thing. -- The applicatiosn could have their own stacks, too;
the multitasker would just need to keep a table of the stack pointer
values of the various applications.

--David A. Lyons  a.k.a.  DAL Systems
  PO Box 287 | North Liberty, IA 52317
  BITNET: AWCTTYPA@UIAMVS
  CompuServe: 72177,3233
  GEnie mail: D.LYONS2