File checkout capability

["Mark C. Widzinski" <Widzinski@sapsucker.scrc.symbolics.com>]

    Date: Thu, 14 Jul 88 11:05 EDT
    From: Scott McKay <SWM@SAPSUCKER.SCRC.Symbolics.COM>

	Date: Tue, 12 Jul 88 10:53:29 pdt
	From: lbaum@BOEING.COM (Larry Baum)


	We are constantly running into the problem of two or more people editting
	the same file simultaneously.  Of course, when we save our files the machine
	does tell us that things are out of sync, but then we must reconcile our
	changes.  

	Does anyone have any code that implements some sort of "check-out" facility
	so that we can be more aware of the fact that someone is already editting
	a file (or even prevents simultaneous editting)?

    In-house and for our Concordia product we have a lock server which
    essentially allows a user on a machine to take a lock on a string.  To
    implement file "check-out", a machine simply takes a lock on the string
    which corresponds to the truename for the file.

    I don't know if I am allowed to send the code out for the so-called
    "Lock Simple" server, since it is now part of a real product.

I'd recommend waiting on distributing this to too many people.  It could
use a little work to make it more robust and less apt to loose locks
when it should maintain them (e.g., when the lock server crashes) or
keep locks when it should loose them (e.g., when the user machine
crashes).

Other than that, I think it should go into the system.