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From: tim@hoptoad.uucp (Tim Maroney)
Newsgroups: comp.sys.mac.system
Subject: Re: Setting System Heap
Message-ID: <11311@hoptoad.uucp>
Date: 5 May 90 09:02:57 GMT
References: <1990May1.231447.29824@agate.berkeley.edu> <1990May3.012140.10133@gaudi.CSUFresno.EDU> <400.264065ea@waikato.ac.nz>
Reply-To: tim@hoptoad.UUCP (Tim Maroney)
Organization: Eclectic Software, San Francisco
Lines: 32

In article <400.264065ea@waikato.ac.nz> ccc_ldo@waikato.ac.nz
(Lawrence D'Oliveiro, Waikato University) writes:
>Files containing INITs (i e those of type "INIT", "RDEV" or "cdev")
>can have a "sysz" resource in them, which specifies the minimum
>amount of contiguous free space that the code will need. The INIT 31
>mechanism will expand the system heap as necessary to fill this need.

Yes, this is correct -- and it's why the sysz suggestions for expanding
the heap won't work in the naive sense that some have suggested.  The
sysz does not add n bytes to the system heap, n bytes being the number
of bytes stored in the resource.  It make sure that there are n
contiguous bytes free in the system heap.

If you run a file which has only a sysz of 50K (and an RTS INIT to make
sure your file runs), then it will check if there are 50K free bytes.
If there are, it will allocate nothing.  But let's say your heap-hacker
INIT does cause the 50K to be allocated, because there isn't enough
free when it runs -- then the storage you've allocated may be used up
later, causing no overall expansion.  If the next INIT wants 50K, then
the next INIT's sysz will act as a no-op, because there are already 50K
bytes allocated.

So, the sysz resource solution can work, but only if you set it to the
total size you want the system heap to be, not the extra size you want
to add.
-- 
Tim Maroney, Mac Software Consultant, sun!hoptoad!tim, tim@toad.com

It is not only fallacious to ignore points, or to answer them solely
with preconceived and contrived arguments:  it is also very, very
rude.  Someone who behaves in this way has only themselves to blame if
things become heated.