Re: config files proposal

[Stephen Leake <stephen_leake@acm.org>]

Darren New <dnew@san.rr.com> writes:

> I think there should also be some sort of tag at the front of each file
> saying it's an Ada config file, even if only
> 
>  -- Ada Grace.Config file V1.0 -- Do not hand-edit.

Part of the point is to _allow_ hand editing :).

> so one could check you've found a proper file and know what version
> it is.

Yes, I'm leaning towards a standard implemntation of config file
versions. If only to hint to application builders that they should
consider versioning issues! It's easy to do in the root tag of an XML
document. 

> > > Yes. Actually, I think the file is OS closed at the end of Open,
> > > after the data is read in.
> > 
> > *That* sounds like an implementation detail to me. Its a good idea
> > perhaps, but still an implementation detail.
> 
> I think it's an important detail for systems where having a file open
> changes the semantics for other users. 

Not for config files. These are _explicitly_ not accessible by
parallel processes.

Hmm. Guess I have to allow read-only parallel access if I'm allowing
system-wide config files. Sigh. Why do things have to be so
complicated?

So yes, the file is closed at the end of an open operation.

> If, for example, you leave it open after you write it, it's possible
> I won't be able to read it. 

Arg. Who gets to write a system config file? This is why I wanted to
exclude parallel access. 

> If you leave it open after reading it, I may be dedicating resources
> on the file server to keeping track of it (assuming it's centrally
> served, for example). Closing it each time would make it easier to
> reason about multiple users using the same config file, and the
> overhead of reopening it should be minimal, given it's a config
> file.

Yeah, I think closing it after each open and flush should be required.

This will still depend on OS file system locking for preventing read
while someone has a file open for write. That is _not_ required by the
config file API, so we can use it on a primitive OS like VxWorks (hmm,
maybe VxWorks has file locking?) or DOS. But it is an added feature of
using a real OS.

-- 
-- Stephe