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From: brian@hpfclm.HP.COM (Brian Rauchfuss)
Newsgroups: comp.sys.mac
Subject: Re: What does access memory manager' mean?
Message-ID: <10620001@hpfclm.HP.COM>
Date: Fri, 9-Oct-87 23:37:33 EDT
Article-I.D.: hpfclm.10620001
Posted: Fri Oct  9 23:37:33 1987
Date-Received: Mon, 12-Oct-87 21:37:30 EDT
References: <5365@jade.BERKELEY.EDU>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 25

/ hpfclm:comp.sys.mac / jmm@thoth14.berkeley.edu.BERKELEY.EDU /  1:41 pm  Oct  8, 1987 /
>In IM, it says that you can't use any
>routines that access the memory manager
>directly or indirectly from within
>things such as VBL tasks, system tasks, etc.
>Does this mean that any system call that
>can cause heap scrambles is disallowed?

    No, it is worse than that, VBL tasks 
are run during the vertical blanking
interval, which is run by an interupt.
That means that the system could have 
been doing ANYTHING when it was interupted.
It could have been rearranging the heap,
for example, in which case memory manager routines
which need to look at the heap are very, very
dangerous.  In general, it is safe to play with
locked down blocks and pointers, and most (all?)
commands which do not scramble the heap can
be used as long as you are sure the data
you pass to them is not moveable.

      Brian (Smokefoot) Rauchfuss

"Hey, lay off man, I'm a scientist"