Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!claris!wombat
From: wombat@claris.com (Scott Lindsey)
Newsgroups: comp.sys.apple
Subject: Multitasking, IIgs etc
Message-ID: <9433@claris.com>
Date: 4 Apr 89 19:34:25 GMT
Organization: Claris Corporation, Mountain View CA
Lines: 34

OK, I've been giving the subject a bit of thought.  I think that a switcher-
like program could be written for the GS.  This might be a first step toward
a Multifinder.  I think these are the only directions really possible if you
want to maintain compatibility with existing desktop applications.  (No, I'm
not saying this just because of AWGS -- I'm approaching it from a Mac point
of view.)

In general, an implementation might work this way.  All switching would go
through GetNextEvent (since the GS doesn't have WaitNextEvent, it's not
quite possible to do Multifinder the way the Mac does).  The only things
that would have to be switcher aware (read: patched by the switcher) are the
Event Manager, the tool Locator, any FooStartup, FooShutdown where Foo is a
tool used by one of the applications and the memory manager.  Finally, NDA's
would have to be treated specially.

On a switch (say through clicking on an icon on the Menu bar) all allocated
memory in bank 0 would be swapped out (except, obviously, for the softswitches)
and the bank 0 info associated with the new app would be swapped in.  If we
assume well-behaved tools, all globals for a tool are on its direct page, so
we only have to worry about loading, starting up, and shutting them down
correctly.  NDA's are another problem.  Since there is only one copy of an
NDA around, it could not remain open across a switch (the window manager
wouldn't remember it :-), so we'd probably either not allow a switch when
NDA's are open or force a close of all before switching.


Obviously, these are just very rough ideas.  I'm open to comments.


-- 
Scott Lindsey     |"Cold and misty morning. I heard a warning borne in the air
Claris Corp.      |    About an age of power when no one had an hour to spare"
ames!claris!wombat| DISCLAIMER: These are not the opinions of Claris, Apple,
wombat@claris.com |    StyleWare, the author, or anyone else living or dead.