Unix File Locks

[David Beckemeyer]

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 at bdt.UUCP)	| "Adios amigos.  And, as they say when 
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