Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!cmcl2!kramden.acf.nyu.edu!brnstnd
From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.unix.programmer
Subject: Re: Determining if an existant file is open
Message-ID: <26251:Nov2119:42:1090@kramden.acf.nyu.edu>
Date: 21 Nov 90 19:42:10 GMT
References: <1990Nov16.023110.1305@csun.edu> <1990Nov16.200945.14468@nusdecs.uucp> <274975C4.21C@tct.uucp>
Organization: IR
Lines: 17

In article <274975C4.21C@tct.uucp> chip@tct.uucp (Chip Salzenberg) writes:
> According to rwhite@nusdecs.uucp (0257014-Robert White(140)):
> >Do the "put process number in lock file" thing as in uucp.
> This approach cannot be used reliably without either (1) having a lock
> held forever by a dead process, which I find unacceptable, or (2)
> using a kernel locking call, which renders the pid file redundant.

It can be used reliably if you put information like pid and date into
the name of the lock file.

> For you doubters: Once you've determined that a lock file is stale and
> you want to unlink() it, how do you know the lock file hasn't been
> replaced in between the decision to unlink() and the unlink() itself?

The old name will never be reused, so there's no danger of replacement.

---Dan