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From: guy@gorodish.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Novice Question -- are sources needed (really merits of Apollo)
Message-ID: <20547@sun.uucp>
Date: Sun, 7-Jun-87 00:33:42 EDT
Article-I.D.: sun.20547
Posted: Sun Jun  7 00:33:42 1987
Date-Received: Sun, 7-Jun-87 18:44:43 EDT
References: <7728@brl-adm.ARPA>
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>     My conclusion is that Suns would definitely have the lowest initial
> capital cost, but they share the disadvantages of pure UNIX with the HP
> and IBM systems.  ... The network-wide operating system has a lot of
> features that Sun's NFS doesn't, critical things like file locking.
> How would you like to make some major changes to a file, and right before
> you saved it, have someone else read the old version into an editor, make
> a minor change, and then write over your changes right after you saved
> your new version?

Some clarification on a couple of points mentioned here.  First, NFS
isn't a network-wide operating system, it's just one of a set of
network services; second of all, there is a file locking facility
that is part of the same suite of network services that NFS belongs
to.  One could imagine an operating system that requires any editor
to use this service to prevent the situation you describe; however,
UNIX isn't such an operating system.  The correct comparison here
isn't DOMAIN, Aegis, DOMAIN/IX, etc. (is there a name for the
software that DOMAIN/IX, and I presume Aegis, sits on top of, or is
DOMAIN/IX considered to be on top of Aegis?) vs. NFS, it's DOMAIN,
Aegis, DOMAIN/IX, etc. vs. UNIX.

Also, for a lot of cases, there are facilities in UNIX that provide
this sort of locking.  If you use a source control mechanism such as
SCCS or RCS, you would normally check a file out for editing, which
would arrange that only you would have permission to write the file,
and prevent anybody else from checking it out for editing.  This is
not as convenient as having the editor lock the file when it is
entered and unlock it when it exits (something that could be done in
most versions of UNIX these days, although the locks provided by UNIX
are generally advisory); however, it would (assuming people honor the
locks) also prevent somebody from writing over your changes in a
transaction that begins after you exit the editor (I presume the lock
that the editor obtains is released when it exits).
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com