Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hoptoad!tim
From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need info on multitasking capabilities on the mac
Message-ID: <9088@hoptoad.uucp>
Date: 27 Nov 89 18:04:31 GMT
References: <9072@hoptoad.uucp> <1554@cbnewsk.ATT.COM>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Eclectic Software, San Francisco
Lines: 41

In article <6391@tank.uchicago.edu> gft_robert@gsbacd.uchicago.edu writes:
>Sounds like it's your comm program, not the Mac OS.  I've never had any
>problems of that nature when downloading (using Versaterm).  I can choose
>menus, play games, etc.  Pretty good multitasking, as far as I'm concerned.

From article <9072@hoptoad.uucp>, by tim@hoptoad.uucp (Tim Maroney):
> I wonder how they do that.  Can anyone provide any information?  My
> first thought was to schedule your file transfer protocol off the
> vertical retrace manager, but your tasks don't get called when you're
> switched out...

In article <1554@cbnewsk.ATT.COM> ech@cbnewsk.ATT.COM (ned.horvath) writes:
>Unless you install the VBL task in the System heap.  See TN 180 for a full
>discussion.

Thanks!  (Although I wonder whether a single brief sentence in a long
and boring technical note really qualifies as "a full discussion".)
This could be used, as long as you're not using the Communications
Toolbox for your file transfers, but rolling your own file transfer
protocols instead.

In re-reading that note, I also discovered that what I said about
device completion routines was wrong.  MultiFinder *will* switch if
there are async device requests pending; it only refuses to switch if
async file requests are pending, not device requests.  So a hand-rolled
file transfer protocol could indeed schedule itself off asynchronous
device manager request completion routines.  Or could it?  It will also
need to do file manager requests, and it doesn't seem safe to do this
either synchronously or asynchronously.  You can't make a synchronous
request from a completion routine or the system could deadlock; you
can't call it asynchronously or you risk confusing MultiFinder -- this
might just be a problem for the user (not being able to switch layers),
not a system-crash-type problem, but I wouldn't like to bet my code
reliability on it.
-- 
Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, tim@toad.com

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