Path: utzoo!attcan!uunet!cs.utexas.edu!usc!apple!Apple.COM!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Identifying real handles
Message-ID: <8613@goofy.Apple.COM>
Date: 7 Jun 90 21:46:25 GMT
Sender: usenet@Apple.COM
Organization: Future Stuff,  Apple Computer, Inc.
Lines: 25
References:<7426@ucdavis.ucdavis.edu> <18379@well.sf.ca.us>

In article <18379@well.sf.ca.us> odawa@well.sf.ca.us (Michael Odawa) 
writes:

> A different check (which I do in my version of ValidHandle) might be to
> determine whether the tag byte on the block header (the first of the 
eight
> bytes which preceed the address) contained 0x8x, as documented in IM 
II-24:

Unfortunately, this isn't 32-bit clean.  The block headers in the 32-bit 
Memory Manager seem to be 12 bytes long (instead of 8).  (I say "seem to 
be" since I was poking around without documentation.)

In addition to the other tests that were mentioned, you might try testing 
whether RecoverHandle(addresss^)=address.  (This is part of MacApp's 
IsHandle check.)  If you do this, you have to be careful because 
RecoverHandle only works if the current heap zone is the same as the 
handle's.  You also have to check for an empty handle (one whose master 
pointer is NIL).

Larry Rosenstein, Apple Computer, Inc.
Object Specialist

Internet: lsr@Apple.com   UUCP: {nsc, sun}!apple!lsr
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