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

From: <ccjason@us.ibm.com>
Date: Thu, 13 Jan 2000 14:15:39 -0500
To: "Geoffrey M. Clemm" <geoffrey.clemm@rational.com>
cc: w3c-dist-auth@w3.org
Message-ID: <85256865.0069D72C.00@D51MTA03.pok.ibm.com>

Wow.  This is dense.  Here goes...


   GULP: Part II

   - A URL identifies a resource.

Cool. I notice there is no mention of null resources.  Perhaps that's
intentional?


   - A lock is on a URL. Every lock has a lock token and a lock owner.

  Every lock on a resource has a name which is a relative URL (i.e. a slash
  separated sequence of URL segments). Every LOCK request that succeeds
  results in a new globally unique lock token. Every lock token has an
owner
  that is the principal of the LOCK request.

Just vocab.  "Name" doesn't seem to be the right word.  I'd expect a "name"
to be unique and be equivalent to a token.  -- Otherwise, A-OK.

  - A LOCK request creates a lock on the request URL.

  When a request of the form "LOCK /pathX" succeeds, a lock named "pathY/."
  with a new lock token is added to the resource identified by "/", where
  "pathY" is the result of applying standard URL path transformations to
  remove all segments named "." or ".." from "pathX". If a collection C has
a
  binding from "segX" to resource R, and a request adds a lock named
  "segX/pathZ" with token "L" to C, then the request adds a lock named
"pathZ"
  with token "L" to R. Similarly, if a collection C has a lock named
  "segX/pathZ" with token "L", and a request (e.g. PUT, COPY, MOVE, BIND)
adds
  a binding in C from "segX" to resource R, then the request adds a lock
named
  "pathZ" with token "L" to R. If the attempt to add the lock named "pathZ"
to
  R fails, the request MUST fail.

I'd prefer not to say the lock is on a URL, but hey, let's give it a
shot....  Oh..
I think I understand what you mean by that. The phrase just threw me off.
You are
talking about what Eric calls namespace locks.

All this does ring of implementation rather than model.  You're basically
describing
how URI protection would have to be implemented to be efficient.  For this
reason,
there is a lot of detail here.  Mention and emphasis of the overall effect
would be
good: URI protection.



   - An UNLOCK request removes all locks with the specified lock token.

   When a request of the form "UNLOCK /pathX; Lock-Token L" succeeds, then
the
   lock with token "L" is removed from the resource identified by "/". If a
   collection C has a binding from "segX" to resource R, and a request
removes
   a lock named "segX/pathZ" with token "L" from C, then the request
removes a
   lock named "pathZ" with token "L" from R.

Hmm.  Couldn't you just say that the lock with token L is removed
everywhere
it existed?  At least as a summary statement?  This rings of implemenation
again.

   Similarly, if a collection has a
   lock named "segX/pathZ" with token "L", and a request (e.g. DELETE,
MOVE)
   removes a binding in C from "segX" to resource R, then a lock named
"pathZ"
   with token "L" is removed from R.

This should be a different bullet. -- Also, we seem to talk of specific
situations.
If so, doesn't the above descriptions also cover the situation for
descendents of
R (assuming R is a collection)?

   - A lock on a URL protects which resource is identified by that URL.

   If a collection identified by the URL "/colX" contains a lock named
"pathZ"
   with token "L", if a request would change the resource identified by
   "/colX/pathZ", the request MUST specify token "L" in an IF header and
the
   request principal MUST be the owner of token "L".

OK.  The "lock on URL" phrase threw me off again, but the details sound
right.

Does this include null mapped resources?  Or are we leaving that issue out
for
now?

Note: this only protects the mapping of the resource explicitly locked.
Not
*necessarily* any of the bindings to the root.  Just an observation.  Later
we might have to decide to allow servers to also protect those bindings if
they wish.

If this is the way we're going to describe the semantics we want, will we
later need to use "If there exists..." type phrasing?

You don't say what will happen if the request does include all the right
tokens and the sumitter is the owner of all those tokens.  That is the
main area where recent proposals semantically distinguish themselves.


  - A Depth:N lock on a URL locks any URL that extends the locked URL by no
  more than N segments.

  If a collection C has a binding to resource R, and a request adds a
Depth:N
  lock named "." with token "L" to C, then the request adds a Depth:N-1
lock
  named "." with token "L" to R. Similarly, if a collection C has a Depth:N
  lock named "." with token "L", and a request adds a binding in C to
resource
  R, then the request adds a Depth:N-1 lock named "." with token "L" to R.
If
  the attempt to add the lock named "." to R fails, the request MUST fail.
  Conversely, the Depth:N-1 lock is removed from R whenever a binding to R
or
  the Depth:N lock is removed from C.

Dynamic depth lccks.  Okay.

I guess technically you have declare what happens at depth 0.




  - A Depth:infinity lock on a URL locks all URL's that extend the locked
URL.

  If a collection C has a binding to resource R, and a request adds a
  Depth:infinity lock named "." with token "L" to C, and this is the first
  Depth:infinity lock named "." with token "L" on C, then the request adds
a
  Depth:infinity lock named "." with token "L" to R. Similarly, if a
  collection C has a Depth:infinity lock named "." with token "L", and a
  request adds a binding in C to resource R, then the request adds a
  Depth:infinity lock named "." with token "L" to R. If the attempt to add
the
  lock named "." to R fails, the request MUST fail.

  If a collection C has a
  binding to resource R, and a request removes the last Depth:infinity lock
  named "." with token "L" from C, then the request removes a
Depth:infinity
  lock named "." with token "L" from R. Similarly, if a collection has a
  Depth:infinity lock named "." with token "L", and a request removes a
  binding in C to resource R, then a Depth:infinity lock named "." with
token
  "L" is removed from R.

Sounds like this wording also handles the recursive removal of locks from
the whole tree.  Good.  -- There is a bit of messiness dealing with loops
I think.  If didn't couch this all in detailed implementation based way,
we might not have to mention that.

BTW, you speak of the "*last* Depth:infinity lock".  What is the
significance of "last".  (I also notice you mentioning "first" earlier.)

  Note that multiple Depth:infinity locks named "."
  with the same token can be placed on the same resource due to multiple
  bindings to that resource in a Depth:infinity locked collection.

Right.  IOW, "do the right thing". :-)



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

  If a request attempts to add a lock named "pathZ" with token "L" and type
T
  to resource R, and R already has an exclusive lock named "pathZ" with
type
  "L" but with a different token, the request MUST fail. Similarly, if a
  request attempts to add an exclusive lock named "pathZ" with token "L"
and
  type T to resource R, and R already has a lock named "pathZ" with type T
but
  with a different token, the request MUST fail.

Hmmm. Exclusivenss of exclusive locks also apply to the name space aspect
of
the lock?  This isn't good.  It means only one exclusive lock can exist in
the
system at a time.  I'd prefer the lock to be shared unless the resource is
at
a lock URI.  (Resource Lock, not Namespace lock)

  - A write-lock on a URL protects the body and dead properties of any
  resource identified by that URL.

  If a resource has a write lock named "." with token "L", in order to
modify
  the body or dead properties of that resource, a request MUST specify
token
  "L" in an IF header and the request principal must be the principal that
  created the lock.

So we now need to define "lock".  Based on how you are using it in this
document,
a LOCK request can create many locks.  And all of those locks will
basically have
the "same" (expanded) name.  Except if it's a depth lock in which case
there might
be a lot of locks with "." as their name so their "expanded" names will
differ.
Anyway, my point here is that a LOCK request creates many "lock"s.  If you
couch
it as you have, I think you're obligated to use Eric's "lock set" term.

You haven't really said what happens in null mapped URI space.  The actual
document
might not need to mention it, but since we've talked a lot about it, you
probably
should clarify that for us on the list.

   OK, Jason, Yaron, Eric, et. al, what did I forget this time? (:-)

Well, overall my impression is that the semantics outlined here so far are
good, but that the explanation is very dense and that it probably
doesn't need to be.   Although a few of the semantic details are differnt,
Eric's way of describing it might be a LOT simplier.  Perhaps starting with
Eric's proposal and altering that match your semantics might work better.


Jason.
Received on Thursday, 13 January 2000 14:16:45 GMT

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