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From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: DA questions, the second time around...
Message-ID: <33466@ucbvax.BERKELEY.EDU>
Date: 4 Jan 90 16:15:45 GMT
References: <68060@tiger.oxy.edu>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 30

In article <68060@tiger.oxy.edu> sonenbli@oxy.edu (Andrew D. Sonenblick) writes:
>I have many a DA which are utilities which must be loaded into the
>application heap (so they can be assured of communication with the appl).
>No biggie, option down on opening the DA.  Ok, but I also *need* the
>DA's to be closed upon quitting the applications they reside in.

I, too, had this problem in the "Flips" desk accessory that is shipped in
Scott Kim's "Letterforms & Illusions" product. This product has close to
100 paint files of Kim's beautiful calligraphic puzzle art, a demo version
of  MacPaint, and my desk accessory that adds new commands to macpaint for
file traversal, and exploring symmetries of rotation and reflection.

I solved the problem by installing a head patch on ExitToShell that, when
triggered, attempts to remove my patches.  (It may not be able to remove 
them, since thwey might have gotten re-patched by something else in the
interim, and that something else will have cached away my procedure
pointers as what it saw as the old value of the traps.) I patch through
small "islands" in the system heap, so if it can't remove them, it can at
least make them innocuous.

I checked, applications _can_ exit via a return from main(), without
directly calling ExitToShell(). But, if they try, the O.S. executes an
ExitToShell() for them.

"Letterforms & Illusions" is published by Scott Foresman & co. Check it
out.

--- David Phillip Oster            --  No, I come from Boston. I just work
Arpa: oster@dewey.soe.berkeley.edu --  in cyberspace.
Uucp: {uwvax,decvax}!ucbvax!oster%dewey.soe.berkeley.edu