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Re: Locking UI comments

From: Mark Benedetto King <mbk_at_lowlatency.com>
Date: 2004-10-14 19:27:05 CEST

On Thu, Oct 14, 2004 at 12:49:20PM -0400, Greg Hudson wrote:
> On Thu, 2004-10-14 at 11:31, Brian W. Fitzpatrick wrote:
> > > Blind LOCKing is something that a normal WebDAV client could do, but that
> > > doesn't prevent us from supporting a LOCK request that does automatic and
> > > atomic update-to-dateness checking; I don't think they're mutually
> > > exclusive.
> >
> > Agreed.
> There's no need to invent extra protocol machinery. The client can
> issue a LOCK request (blowing out if someone else already holds the
> lock), then check for up-to-dateness, and then release the lock if it's
> not up to date. This is perfectly atomic.

At the time I was thinking that the need for an explicit release
could cause locks to be leaked in the event of network/kernel/application
interrupts after the lock acquisition but before the release.

I realize now that since we don't 2PC the operation, even my more
"test and set" oriented approach is insufficient to prevent lock leaks.

Considering that "rm -rf wc" is enough to also leak the lock, and that
the locking system already includes the capability for users to handle
the case of abandoned locks, I think it makes sense to consider these
potentially leaked lock references as simply unintentionally abandoned.

IOW, I agree.


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Received on Thu Oct 14 19:26:49 2004

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