Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!decwrl!decvax!spray!anson
From: anson@spray.CalComp.COM (Ed Anson)
Newsgroups: comp.sys.mac
Subject: Re: System 8.0: no more DA's.
Message-ID: <2556@spray.CalComp.COM>
Date: 3 Jan 89 15:48:55 GMT
References: <1988Dec14.223739.16280@cs.rochester.edu> <321@internal.Apple.COM> <6692@polyslo.CalPoly.EDU> <33613@think.UUCP>
Reply-To: anson@spray.UUCP (Ed Anson)
Organization: CalComp, A Lockheed Company, Hudson, NH, USA
Lines: 25

In article <33613@think.UUCP> barmar@kulla.think.com.UUCP (Barry Margolin) writes:
>
>Stuffit is a "buggy app" according to Apple's (or at least Phil's)
>definition.  Applications are supposed to call into the system
>frequently, even if they aren't looking for an event for themselves.

There are probably lots of "buggy" applications, by this definition. One of
the problems is this: There are some ROM calls which can require more time
to execute than the maximum time that should be allowed between opportunities
for task switches. DrawPicture comes to mind. Or any I/O call to a slow
device, or one which may pause between characters. I have had to modify
drivers to provide time-outs, just to work around this latter problem.

On the other hand, adding preemptive multi-tasking would make subtle but
important changes to the programming model. I'm not sure we're ready for the
effects that would have on existing applications. Most applications have
come to rely on the fact that certain global system state elements don't
change except at well-defined times. Preemptive multi-tasking would break
such applications.  When it does come, preemptive multi-tasking will 
probably require specific enabling by each participating application, much
as background operation does now.
-- 
=====================================================================
   Ed Anson,    Calcomp Display Products Division,    Hudson NH 03051
   (603) 885-8712,      anson@elrond.CalComp.COM