Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!tut.cis.ohio-state.edu!ucbvax!hoptoad!tim
From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Think C 4.0 questions
Message-ID: <10160@hoptoad.uucp>
Date: 10 Feb 90 20:27:17 GMT
References: <10682@bsu-cs.bsu.edu> <1968@cbnewsk.ATT.COM> <10111@hoptoad.uucp> <90039.151841CXT105@PSUVM.BITNET>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Eclectic Software, San Francisco
Lines: 31

In article <10111@hoptoad.uucp>, tim@hoptoad.uucp (Tim Maroney) says:
>>Why do you say FSWrite can move memory?  It's not in the lists, so unless
>>it's in an unlocked segment, I don't see how (or why!) it would move memory.

In article <90039.151841CXT105@PSUVM.BITNET> CXT105@psuvm.psu.edu
(Christopher Tate) writes:
>According to Apple, the operating system has been patched from here to
>hell and back again, and the lists are no longer valid.  A much safer
>way to go is to assume that any trap routine can move memory, and set
>things up to deal with this possibility.

FSWrite isn't even a trap, so it can't be patched.  It's a front-end to
the PBWrite trap.  I can assure you that the traps which have an argument
for asynchronous calling will always be callable at the interrupt level,
and therefore they will never move memory.

>Of course, this can be a real problem when you're trying to carefully
>optimize things, or when you have to get down-and-dirty with the OS, but
>it seems to me like a dandy way to ensure future compatibility....

It can also be a real problem in routine code writing.  I would hate to
think that I was supposed to start locking my handles before calling
BlockMove or TickCount or PBWrite (synchronously).  In real life,
that's not going to happen; there are many traps which clearly will
never move memory.
-- 
Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, tim@toad.com

"Our newest idol, the Superman, celebrating the death of godhead, may be
 younger than the hills; but he is as old as the shepherds."
    - Shaw, "On Diabolonian Ethics"