Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!uwmcsd1!ig!agate!ucbvax!hplabs!well!ewhac
From: ewhac@well.UUCP (Leo L. Schwab)
Newsgroups: comp.sys.amiga
Subject: Re: Sample Exception Handler
Summary: Caveats
Message-ID: <6637@well.UUCP>
Date: 27 Jul 88 10:04:48 GMT
References: <3447@louie.udel.EDU>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: Bleep Gzorp!
Lines: 36
Quote: "There's no time in space!  Hold on!  FLOOR IT, SULU!"  -- Portnoy

In article <3447@louie.udel.EDU> iphwk%MTSUNIX1.BITNET@cunyvm.cuny.edu (Bill Kinnersley) writes:
>Well, I guess I answered my own question out of necessity.  Here is
>my attempt at writing an Exception Handler.  [ ... ]
> [ code deleted ]

	Congratulations, you got it.  I would recommend that you also
restore the tc_ExceptCode pointer when done as well; it may be important to
someone.

	There are some caveats that you should be aware of.  Kickstart does
not internally interlock asynchronous operations.  When you enter a
Kickstart routine, the routine assumes that it will run to completion before
returning to you.  Thus, certain Kickstart routines may procure some
resources upon entry, and free them upon exit.  If you interrupt them and
don't return, Bad Things will happen.

	As an example, suppose you call Draw().  Draw() calls OwnBlitter(),
then performs weird sex on the blitter to draw the lines.  If, during this
time, your exception routine gets called, and your exception routines calls
exit() or longjmp(), or in any way fails to return back to where it came
from, you will have left the blitter allocated (since Draw() never got a
chance to call DisownBlitter()).  If you exit(), the system will appear to
stop, since no one can get control of the blitter again.  Similar situations
exist in DOS.

	As long as your exception routine returns without trying to re-route
the execution thread, you can use exceptions safely.  However, be very
careful of interrupting Kickstart routines; weird things may happen.

	You may wish to look at Matt Dillon's Qint routines which help
alleviate this problem.

_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
Leo L. Schwab -- The Guy in The Cape	INET: well!ewhac@ucbvax.Berkeley.EDU
 \_ -_		Recumbent Bikes:	UUCP: pacbell > !{well,unicom}!ewhac
O----^o	      The Only Way To Fly.	      hplabs / (pronounced "AE-wack")
"Hmm, you're right.  Air is made up of suspended meat loaf."  -- Josh Siegel