Path: utzoo!mnetor!uunet!husc6!mailrus!ames!amdahl!nw
From: nw@amdahl.uts.amdahl.com (Neal Weidenhofer)
Newsgroups: comp.lang.c
Subject: Re: longjmp() from nested signal handlers
Message-ID: <26739@amdahl.uts.amdahl.com>
Date: 5 Apr 88 21:11:54 GMT
References: <4548@june.cs.washington.edu>
Organization: Amdahl Corporation, Sunnyvale CA
Lines: 30
Summary: longjump from a signal handler ALWAYS results in undefined behavior

In article <4548@june.cs.washington.edu>, pardo@june.cs.washington.edu (David Keppel) writes:
> I also don't understand why jumping out of a nested signal handler
> is different from jumping out of a non-nested handler.
> 
>     pardo@cs.washington.edu	..!ucbvax!uw-beaver!uw-june!pardo

It isn't.  Using longjump from a signal handler ALWAYS results in
undefined behavior.

My favorite example is to consider the case of the signal being
raised while the program is in the middle of malloc(3) (for UN*X
types--something equivalent if you're using VMS or some other
OS).  There is NO WAY that your program is going to continue to
run correctly after control has been forcibly removed from some
routine while its internal tables are in an inconsistent state.

This is why dpANS limits signal handlers to setting a flag and
returning.  Most compilers and/or OS's are going to have to do
some work even to get this right.

The opinions expressed above are mine (but I'm willing to share.)

			Regards,
				Neal Weidenhofer
Nothin' ain't woth nothin'      ...{hplabs|ihnp4|ames|decwrl}!amdahl!nw
   But it's free.               Amdahl Corporation
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