Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!oliveb!apple!darin
From: darin@Apple.COM (Darin Adler)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Toolbox Gotchas (LONG)
Message-ID: <1467@internal.Apple.COM>
Date: 20 Apr 89 07:45:07 GMT
References: <10050096@accuvax.nwu.edu>
Organization: Apple
Lines: 28

In article <10050096@accuvax.nwu.edu> jln@accuvax.nwu.edu (John Norstad) writes:
> Gotcha #3. Don't believe Inside Macintosh.
> 
> On page IM II-34 we read the following warning in the description of the
> HandleZone routine: "If handle h is empty (points to a NIL master pointer),
> HandleZone returns a pointer to the current heap zone."  This is false -
> HandleZone properly returns a pointer to the heap zone that contains the
> master pointer.  See Gotcha #2 above.

This is incorrect. Since the publication of Inside Macintosh Volume II,
HandleZone has been *slightly* enhanced (along with the rest of the
Memory Manager) to handle the system heap as a special case. The sentence
could be correctly reworded: "If handle h is empty (points to a NIL master
pointer), HandleZone returns a pointer to the current heap zone, unless
the handle points somewhere within the system heap zone and the current
heap zone is the application heap zone, in which case it returns a pointer
to the system heap zone."

This could return suprising results, since you can create a heap zone
in the middle of the system heap (in a nonrelocatable or locked relocatable
block), and HandleZone will return misleading values. This hack in the ROM
(and in system patches) lets you be somewhat haphazard about what the current
zone is as long as you stick mostly with the system heap and the application
heap.
-- 
Darin Adler, System Software Scapegoat, Apple Computer
	Internet: darin@Apple.com
	UUCP: {nsc,sun}!apple!darin