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From: lsr@apple.UUCP (Larry Rosenstein)
Newsgroups: net.micro.mac
Subject: Re: !!!!???? I GOT A MAC ATTACK ????!!!
Message-ID: <3667@apple.UUCP>
Date: Sat, 20-Jul-85 16:04:33 EDT
Article-I.D.: apple.3667
Posted: Sat Jul 20 16:04:33 1985
Date-Received: Sun, 21-Jul-85 23:29:28 EDT
Reply-To: lsr@apple.UUCP (Larry Rosenstein)
Distribution: net
Organization: Advanced Development Group, Apple Computer
Lines: 31

In article <9098@ucbvax.ARPA> grady@ucbvax.UUCP (Steven Grady) writes:
>It seems to me that the Switcher could be modified to jump between
>tasks, running all of them (thus concurrently).

The version of Switcher after 2.9 (I believe) support a rudimentary
form of multitasking.  An application can arrange to have one of its
procedures called periodically by the Switcher while it is switched
out.

When Andy Herzfeld implemented this, he tried to provide an option so
that the application could be switched in (except for the screen)
before the procedure was called.  He ran into some problems because of
the time needed to do the switch and the necessity for turning
interrupts off.  So in the final implementation, the application does
not get switched in.

This means that the application has to be very careful about what is
does.  It must locate its heap zone in the Switcher's data structures
and do any allocations on that zone.  It must realize that its
low-memory globals are not switched in, etc.  But for applications
that are well-behaved, the feature does work.

All this will be documented in Inside Switcher that Andy is currently
writing.

-- 
Larry Rosenstein
Apple Computer

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