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RE: Locks and loopback bindings

From: Jim Whitehead <ejw@cs.ucsc.edu>
Date: Tue, 7 Dec 2004 16:32:47 -0800
Message-Id: <200412080032.iB80WtL9027015@cats-mx2.ucsc.edu>
To: "'WebDAV \(WebDAV WG\)'" <w3c-dist-auth@w3.org>

> I'm still not sure why you call that a "problem". As far as I 
> can tell, it works exactly as designed.

Here is a plausible scenario that outlines why I think this is a problem.

Assume there is a collection hierarchy rooted at a collection with
non-unique pathname /collA/collB/collC/collD. Within this hierarchy there is
one loopback binding to /collB/, one of approximately 500 bindings within
the collD hierarchy. There is only the one loopback binding in the entire
collD hierarchy.

Alice wants to work on the /collA/collB/collC/collD hierarchy, and wants to
ensure she can make changes to multiple documents to ensure their contents
are consistent with one another. (Alice should probably be using DeltaV
workspaces for this, but that's another matter). So, Alice depth locks the
entire hierarchy, by submitting her lock request to
/collA/collB/collC/collD.

Bob knows that Alice is working on /collA/collB/collC/collD because they
talked about her doing so at their staff meeting in the morning. So, he was
surprised to discover that the area where he was supposed to work,
/collA/collB/collE/collF, is locked by Alice. Bob phoned Alice and asked her
why she had locked his work area, and Alice replied that she hadn't, and was
confused as to why Bob thought this. Bob replied that his authoring tool
reported her as owning the locks on those resources, and that she had locked
his entire resource space.

Alice uses WebDAV Explorer to unlock /collA/collB/collE/collF (good thing
DAV Explorer automatically retrieves and applies the lock token it finds in
the lockdiscovery header, otherwise Bob and Alice would really have a hard
time :-) However, she's then confused as to why the locks on her resource
space have disappeared. So she locks /collA/collB/collC/collD, only to find
out that she can't take out the lock anymore. Frustrating. She asks Bob if
he was able to take out a lock. Yes, he says, now I'm able to take out the
lock and work.

Strange, thinks Alice, it's as if the system only allows one of us to work
at a time. Not understanding what is going on, and have received no error
messages from her software that would lead her to think that a loopback
binding is causing the problem, she calls her firm's technical support.
Since most existing hierarchy browsers for WebDAV do not give any visibility
into loopback bindings, it's anyone's guess as to how long it will take
technical support to determine the root cause of the problem.

- Jim
Received on Wednesday, 8 December 2004 00:37:39 UTC

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