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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Config_Files proposal
Date: 24 Jun 2002 09:20:08 -0400
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"Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:

> I'd like to understand how to do some form of file lock-out for simultaneous
> access by different processes without immediately getting into some kind of
> OS dependant code. 

You can't; file locking is OS dependant.

However, that in itself is ok for Config_Files. There is no
_requirement_ that it be possible to implement Config_Files in an OS
independent way. It would be nice, of course.

> I can imagine a variety of semaphore schemes that will depend on the
> OS or at least semi-portable facilities, but if the objective is to
> to it strictly within the bounds of Ada, I can't think of a way to
> do that.

That is _not_ one of the objectives. The main objective is to produce
something useful; sometimes that requires OS dependence.

> If the goal is pure, portable, run-anywhere Ada code, I'm betting
> that it will come down to "Don't do simultaneous access - it would
> be Bad..."

Not the goal.

My objection to getting into file locking is twofold:

1) It's complex, and hard to get right.

2) The registry already does it, so use that if you need it.

I believe there are many applications for config files that don't need
file locking. But I'm willing to be convinced otherwise. 

-- 
-- Stephe