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Re: a Grand Unified Locking Proposal (GULP, or perhaps, GULP! :-)

From: Geoffrey M. Clemm <geoffrey.clemm@rational.com>
Date: Fri, 14 Jan 2000 08:52:21 -0500
Message-Id: <10001141352.AA23127@tantalum>
To: w3c-dist-auth@w3.org
   From: "Eric Sedlar" <esedlar@us.oracle.com>

   You want to avoid having name and resource locks as separate entities, so
   you basically say that a name lock (as in my proposal) locks the resource it
   is bound to, if any.


   If the lock is exclusive, you can't lock any other
   name applied to that resource.  For example, if I have /a/foo.html and
   /b/foo.html both identifying the same resource, if I exclusive lock
   /a/foo.html, I can't protect the name "/b/foo.html" since I can't lock it.

You cannot apply an exclusive lock of the same type to /b/foo.html,
but if you just wanted to protect the name /b/foo.html, you could
request a lock of a different type on /b/foo.html (exclusivity is
lock-type specific).

Alternatively, if your server only supports one kind of lock type, you
could lock /b/foo.html/dummy-namespace-lock, which would have a similar effect
(and does not conflict with the exclusive lock already on /b/foo.html.

   Since the LOCK protocol request currently doesn't distinguish between name
   and resource locks, you couldn't lock /b/foo.html anyway (which is why you
   are ok with the restriction above), since the protocol request would try to
   lock the resource identified by /b/foo.html as well as the name.

GULP does not distinguish between "locking the resource" and "locking the
name", although it does distinguish "a lock whose target is X/." and 
"a lock whose target is ."

   However, it does seem like there will be reasons to protect the namespace in
   this way, and I think you are paying a price for reducing the number of

If you wanted to introduce a "namespace lock", you could do so with the
standard lock extension mechanism (i.e. allow both "write" and "namespace"
locks), but that is different from saying there are two different kinds
of locks in the underlying locking model.

   > - If an exclusive lock identifies a resource, no other lock of that type
   > identify that resource.

Note that I have modified this statement to read:

- If a resource has an exclusive lock, that resource cannot be locked
with another locks with the same type and target but a different

This ties the semantics to the lock state of a single resource, rather
than using the vaguer concept of "the resource identified by a lock".

   Here's a scenario: it seems like if application A has an exclusive lock on
   /a/foo.html (say because it is planning on updating the resource to create a
   new version, and it wants to prevent lost updates) and application B wants
   to only read /b/foo.html and protect the namespace so that it can find it
   again later, application B cannot create a shared lock on /b/foo.html,

They can add a lock with a different type from the exclusive lock,
or if there are no other lock types available, they can do the "dummy lock"
approach of locking "/b/foo.html/dummy-namespace-lock".

   The problem is that application A will not actually update the
   resource that app B is working with--it will just create a new revision.
   (Although this may affect the revision selected by app B).  Is this an issue
   your versioned locks deal with?

Versioning is (of course :-) somewhat trickier.  A lock in the presence of
versioning isn't so much concerned with locking the state of a resource
(the majority of the visible resources will be checked-in revisions, and
couldn't be modified even if you wanted to), but rather is concerned with
locking the target selection (so that you don't end up effectively getting
a namespace or state change because new revisions are selected).  This
issue (as you suggest) is addressed with the "revision selection freezing"
I've proposed for the versioning protocol.

Received on Friday, 14 January 2000 08:52:24 UTC

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