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From: wjb%cogsci.COG.JHU.EDU@vm1.nodak.edu
Newsgroups: comp.os.minix
Subject: Re: File locking in MINIX and UNIX
Message-ID: <44837@nigel.ee.udel.edu>
Date: 16 Feb 91 18:25:17 GMT
Sender: mmdf@ee.udel.edu
Lines: 20


>Well, some Unixes support *voluntary* file locking, that is, the OS will
>tell you if a file is locked only if you ask, but it's not enforced.
>Also, the first process has to explicitly lock the file, and the second
>process has to explicitly ask if the file is locked.  Regardless of
>whether the file is locked, the second (any any other) process(es) may
>open the file and do with it as they please.

	Actually some Unices have *mandatory* locking, but this was not
included in POSIX.  If people are interested look up fcntl() in the POSIX
standard.  The rationale they give for not including mandatory locks was the
varied methods used on different systems and the difficulty of implementing
it on systems that support memory mapped IO...

					Bill Bogstad

P.S. to original starter of this thread (whose address I lost) Everything in
my private e-mail to you was correct for some version of UNIX, (just not
POSIX). :-) Just think of this as another example of UNIX assumming that the
user/programmer knows what they are doing.