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From: david@bdt.UUCP (David Beckemeyer)
Newsgroups: comp.unix.wizards
Subject: Unix File Locks
Message-ID: <538@bdt.UUCP>
Date: 5 Apr 89 16:58:26 GMT
Distribution: na
Organization: Beckemeyer Development Tools, Oakland CA
Lines: 23


For years I've seen a lot of Unix code that uses "lockfiles".  It is
often of the form:

	if (stat(lockpath, &statbuf) == 0) 
		return(-1);	/* lock failed */	

	if ((lock_fd = creat(lockpath, 0600)) < 0)
		return(-1);	/* error */

	/* lock succeeded */

My question is:  Isn't there a race condition between the stat and creat?

I've seen this type of code all over the place and I've never understood
why it works.

Excuse me if this has come up thousands of times before; I've never seen it.
-- 
David Beckemeyer (david@bdt.UUCP)	| "Adios amigos.  And, as they say when 
Beckemeyer Development Tools		| the boys are scratching the bad ones,
478 Santa Clara Ave. Oakland, CA 94610	| 'Stay a long time, Cowboy!'"
UUCP: {uunet,ucbvax}!unisoft!bdt!david	|                  - Jo Mora