Xref: utzoo comp.bugs.sys5:670 comp.unix.wizards:12156 comp.unix.questions:10099
Path: utzoo!attcan!utgpu!utstat!geoff
From: geoff@utstat.uucp (Geoff Collyer)
Newsgroups: comp.bugs.sys5,comp.unix.wizards,comp.unix.questions
Subject: Re: ln(1) and System V
Message-ID: <1988Nov6.074740.25667@utstat.uucp>
Date: 6 Nov 88 07:47:40 GMT
References: <1808@desint.UUCP>
Organization: Statistics, U. of Toronto
Lines: 14

I see a race in Geoff Kuenning's inventive solution to locking with
ln(1) on System V:

>	trap "" 1 2 15
>	touch lock
>	ln lock lock1  ||  exit 1
>	trap "rm -f lock lock1; exit 1" 1 2 15

If the "rm -f lock lock1" runs in one copy of this script just after the
"touch lock" runs in another, then the ln will fail unnecessarily.  The
race can be fixed by simply not removing "lock", since "lock1" is the
real lock.
-- 
Geoff Collyer	utzoo!utstat!geoff, geoff@utstat.toronto.edu