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From: ken@CS.Cornell.EDU (Ken Birman)
Newsgroups: comp.sys.isis
Subject: Re: More on use of kill() to detect process failures
Message-ID: <1991Jun28.132439.12920@cs.cornell.edu>
Date: 28 Jun 91 13:24:39 GMT
References: <1991Jun25.120346.21111@cs.cornell.edu> <2869F793.4F50@tct.com>
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In article <2869F793.4F50@tct.com> chip@tct.com (Chip Salzenberg) writes:
>... on System V, you can kill with the pseudo-signal zero.
>This feature provides a "process exists" test.

This is really interesting!  I would appreciate it if ISIS users could
do the following and let me know if they get the "wrong" result
	% kill -0 12345 (any non-existent process id)

On SUN OS I get "Non existent process id", which is just what I would
hope for.  If anyone gets "Bad signal number", let me know what type of
UNIX system you are on.

I feel a bit uncomfortable relying on a non-documented UNIX feature,
but there are definite advantages to having a fall-back way to detect
failure.

I checked and on SUN OS, at least, the debugger never sees an
interrupt when you use signal 0.  In contrast, signal IO definitely
causes debugger activity, and even if there is a way to tell gdb
to ignore it, most ISIS users would find that pretty annoying.

So, thanks for a great suggestion!

(Also, thanks to Max Heffler and Compaq for contribuing their 386
version of ISIS -- I know this was a lot of work for them and I
hope that ISIS users will find it valuable.  The same version of 
ISIS should be fairly easy to move to the SCO UNIX, for those who
prefer SCO to straight System V)

-- 
Kenneth P. Birman                              E-mail:  ken@cs.cornell.edu
4105 Upson Hall, Dept. of Computer Science     TEL:     607 255-9199 (office)
Cornell University Ithaca, NY 14853 (USA)      FAX:     607 255-4428