Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!iuvax!purdue!bu-cs!dartvax!eleazar.dartmouth.edu!earleh
From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How to indicate Out Of Memory
Message-ID: <14215@dartvax.Dartmouth.EDU>
Date: 5 Jul 89 17:06:17 GMT
References: <9866@brunix.UUCP>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Organization: Thayer School of Engineering
Lines: 37

In article <9866@brunix.UUCP> man@cs.brown.edu () writes:
>I've written a program which allocates memory using NewHandle and
>SetHandleSize.  I have my own routines UtilNewHandle and
>UtilSetHandleSize which call the toolbox routines and then check
>MemError() to see if the call succeeded.  When I detect an
>out-of-memory condition, I'd like to put up an alert box and then
>abort.  I have two problems:

     A problem with this approach is that the Toolbox and Operating
System need to allocate space in your application's heap, in addition
to what you use directly.  When you only check for out-of-memory, you
run the risk of not having enough of a free memory pool around for
many system calls to succeed.  How big your pool of free space should
be is something you will probably have to determine empirically, but
you will need one.

     One possible solution, since you process memory requests through
your own filter routines, is to check the amount for free memory
before calling NewHandle and SetHandleSize.  If you see that memory is
getting low, then you can warn the user with an alert before operation
becomes unsafe.  If you make sure that the free pool is always big
enough, then you will not get memory-related system errors, and you
will have enough memory to put up the alert box.  This is more
friendly to the user than waiting until memory requests fail before
you take action.

     Another option is to reserve a largish block of memory which can
be released if things get tight.  You can use a GrowZone procedure to
release this block, thereby making the space available to system
routines.  When the GrowZone procedure is called, then you release the
block, assuring that the current memory request succeeds, but you also
set a global variable to indicate that future requests have a chance
of failure.

Earle R. Horton
"People forget how fast you did a job, but they remember how well you
did it."  Salada Tag Lines