Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!umich!ox.com!heifetz!tbomb!time
From: time@ice.com (Tim Endres)
Newsgroups: comp.mail.misc
Subject: Re: Will ELM ever use lockf()?
Message-ID: <01CE0001.cmjkhe5@tbomb.ice.com>
Date: 13 Apr 91 16:22:28 GMT
Reply-To: time@ice.com
Organization: ICE Engineering, Inc.
Lines: 26
X-Mailer: uAccess - Mac Release: 1.1.b1


In article <1991Apr11.024849.29924@Veritas.COM>, tron@Veritas.COM (Ronald S. Karr) writes:
> >Failure scenario:
> >  Process A owns lockfile - Processes B & C are contending for one.
> >  B reads A's PID from lockfile.
> >  A finishes, removes lockfile and exits.
> >  B sends signal 0 to A's PID, notes that process is gone.
> >  C notes that no lockfile is present and creates one.
> >  B removes lockfile (now belonging to C) and creates one.
> >  At this point both B and C think they have exclusive access to
> >  the mailbox.
> 
> However, both smail3 and elm create the files using the O_EXCL flag,
> indicating that the OS should ensure that only one of the two creates
> should succeed.

I do not understand this. If B is removing the lock file created by
C, how would the O_EXCL flag stop B from creating its lockfile?

tim.

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