Path: utzoo!utgpu!watserv1!watmath!att!ucbvax!ucdavis!iris!lim
From: lim@iris.ucdavis.edu (Lloyd Lim)
Newsgroups: comp.sys.mac.programmer
Subject: Identifying real handles
Message-ID: <7426@ucdavis.ucdavis.edu>
Date: 4 Jun 90 13:44:08 GMT
Sender: usenet@ucdavis.ucdavis.edu
Reply-To: lim@iris.ucdavis.edu (Lloyd Lim)
Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
Lines: 39

This is perhaps not the best thing to do on a Mac but I need to be able to
tell if some arbitrary long is a real handle in the System heap or the current
app heap.  I want to keep it relatively clean so I don't want to go looking
through the heap's internal structures.  Currently, I use the following code:

Boolean ValidHandle(address)

register long address;

{
   register Boolean  valid;
   register THz      heapZone;
   
   valid = FALSE;
   if (address && !(address & 1)) {
      heapZone = HandleZone(address);
      if (!MemError() && (heapZone == SystemZone() ||
                          heapZone == ApplicZone())) {
         valid = TRUE;
      }
   }
   return(valid);
}

The problem is that this routine can get passed any arbitrary long and that
some values seem to cause a bus error with HandleZone.  I say "seem" because
I haven't been able to find a value which causes a bus error in a test program
but bus errors do occur in the real situation if enough values are examined.
The real situation is practically unobservable.

Any ideas on a better way?  If you try doing extra checking before calling
HandleZone, you'll get bus errors right away when you do (*(Ptr) address).
If there is a solution that isn't right 100% of the time but doesn't cause
bus errors, that would also be ok.

+++
Lloyd Lim     Internet: lim@iris.ucdavis.edu (128.120.57.20)
              Compuserve: 72647,660
              US Mail: 146 Lysle Leach Hall, U.C. Davis, Davis, CA 95616