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Subject: Re: [wsrp] Session scoped transient properties.



This likely revolves around how one views idempotency and the WSRP protocol.

It has been frequently argued that there is a straight-forward mapping of the HTTP verbs to WSRP operations and, in particular, that getMarkup and getResource are idempotent operations. Whether one agrees with that assertion or not, there is the next level of issue in that many sites relax idempotency to only include transactional items and not 'trivial' things (such as hit counters) or the caching of items in a user session. It is often these use cases that drive container decisions to not enforce the idempotent requirements of certain interactions, but rather to pass the issue on to component developers. At this philosophical level, a key question is whether adding the ability to return transientProperties with response to GM and GR wouldn't be a declaration that these aren't really idempotent interactions. (The "container" is allowing non-idempotent behavior without knowledge as to whether it will be used in a "transaction" manner ... and components can not determine this either.)

On a practical level, it seems like adding this feature would cause page refreshes to exhibit unexpected behavior. Consider when portlet A generates its markup and then portlet B updates a transient property both receive. A page refresh would cause a change in the markup from portlet A which would likely be unexpected in many cases and would definitely exhibit that the page wasn't conforming to idempotent requirements. I'm not sure this is entirely a bad thing, but it shouldn't be taken lightly either.

Rich



Michael Freedman <michael.freedman@oracle.com>

03/21/06 04:28 PM

To
wsrp <wsrp@lists.oasis-open.org>
cc
Subject
[wsrp] Session scoped transient properties.





Currently we don't allow getMarkup and getResource to return
transientPropertyUpdates; only performBlockingInteraction and
handleEvents can.  Should we remove this restriction?

Currently, we don't allow navigational state, mode, window state changes
from getMarkup/getResource because we can't ensure the consumer can
implement reasonable semantics.  To a lesser extent we disallow this
because our model discourages state changes during render.  However,
because we can't control internal producer session state this is a
convention not something that can be fully enforced.

I believe setting transient session properties at GM/GR time can be
semantically defined -- its no different then doing such a thing locally
in a concurrent world.  I.e. the consumer honors such sets immediately
[as with handleEvents].  So, though we would continue to want to
discourage transient property state changes should we prevent it merely
on the grounds that its not our preferred model?

What we lose by having this restriction are degrees of freedom in how
environments built on top of wsrp that ease portlet development will
expose this concept.  One reasonable model [that JSR 286 is currently
advocating] is to not distinguish within portlet code between transient
session properties and producer session properties.  From a code
perspective there are just session properties.  The code reads/writes
these values without explicit knowledge as to whether the value is
shared with the consumer.  That detail is described in
configuration/metadata. The JSR 286 container is responsible for moving
the appropriate values to/from the session from/to the consumer.  Like
wsrp, the jsr discourages session state changes during
render/getresource.  Also like wsrp it doesn't prevent such changes.  
With the current restriction the JSR is faced with either tightening its
requirements to throw an exception if any session writes are attempted,
allowing the local writes but throw an exception for those session
properties that are shared [transient], or merely updating the values
locally but not returning such state to the consumer [meaning these
updates will be lost on the next request as the transient properties are
pushed again with the old values].  All three of these are behaviors
will be foreign to java [web app] developers.
  -Mike-



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