On Mon, 23 Aug 1999, Christopher Masto wrote:
> > The thing about well-intentioned but incorrect locking code is that
> > it will appear to work fine, until it trips over the one code path
> > where it forgets to lock some file that it should have locked. And
> > even then, the code will "work" just fine, until multiple processes
> > are accessing that file at the same time.
> >
> > I think it is appropriate for an operating system to provide an option
> > such that *it* (the system) will enforce the locking, and not have to
> > trust that all code-paths in all programs will do the right thing
> > WRT advisory locking.
>
> Dunno about that.. if you're using advisory locking, you know to say
> "lock the file, then read the data, do your calculation, write it out,
> and unlock". This manditory locking sounds like an invitation for
> disaster. "I don't need to pay attention to the details because
> the kernel will take care of it for me."
>
> Actually, I don't really understand the paradigm. Two processes need
> to safely update a file, so one of them aquires a mandatory lock, and
> the other.. uh.. just blocks trying to open the file? How does it
> know it's not the first one?
It means that if user A puts data in (and follows locking procedure
correctly) then he doesn't have to worry that user B might not be
following correct locking procedure, because user B is mandatorily
forced to follow the procedure. There isn't any added sloppiness, just
a guarantee that if one user locks a file, no other rogues can get into
it while the lock exists.
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Chuck Robey | Interests include any kind of voice or data
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