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From: dorner@pequod.cso.uiuc.edu (Steve Dorner)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Large Programs and Memory Management Questions
Message-ID: <1991Apr24.170354.20749@ux1.cso.uiuc.edu>
Date: 24 Apr 91 17:03:54 GMT
References: <1991Apr24.122618.13791@bmers95.bnr.ca>
Sender: usenet@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at U-C
Lines: 42

>There is the "unload all your segments every time through your event loop"
>effective method or are there other better methods?

If you know your code in and out, you could unload segments on the fly.  Just
be darn careful you don't unload a segment that holds anything on the
current call stack.  You're PROBABLY better off not doing this, unless
you have a very special program, since it will require you to do a lot
of careful bookkeeping on what routines call what and what segments
they're in, and will probably not gain you much anyway.
 
>Should your application periodically compact the heap to keep it from
>getting fragmented?

No.  Won't do you any good.  Just make sure you don't have relocatable
blocks lying around and you'll be fine.

>What would happen if there was not enough memory to load a CODE segment?

La Bombe.

>And more importantly, how do you prevent
>this from happening

There are a couple of ways.  You can reserve a goodly chunk of memory, and
release it in your GrowZone procedure; this will cover your posterior often.
The other way is to have intimate knowledge of inter-segment references,
and always preflight such calls by checking if there is enough memory
to load the needed segment.  I think MacApp does this.  I doubt it's practical
for the average developer, unless you come up with an elaborate segmentation
system.

  if (EnoughMemoryForCodeSegment(32)) CallSomeFunction(withSomeArg);
  else RefusePolitely();

would get real old if it weren't being done automagically by your development
environment.

I'd suggest you get a copy of "How to Write Macintosh Software" by Scott
Knaster.  It's a big help with issues like this.
--
Steve Dorner, U of Illinois Computing Services Office
Internet: s-dorner@uiuc.edu  UUCP: uunet!uiucuxc!uiuc.edu!s-dorner