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Subject: RE: [wsrp] spec-2.0-draft-05: events and blocking actions

Two comment bellow, marked with <YT>.




From: Rich Thompson [mailto:richt2@us.ibm.com]
Sent: Tuesday, March 08, 2005 8:49 PM
To: wsrp@lists.oasis-open.org
Subject: RE: [wsrp] spec-2.0-draft-05: events and blocking actions


Comments in-line


"Spector, Artem" <artem.spector@sap.com>

03/08/05 12:59 PM






RE: [wsrp] spec-2.0-draft-05: events and blocking actions




Some more thoughts about event handling:

1.                 Separate between event generations. If a Consumer during
distribution of some events (current generation) gets a response with a
new portion of events (new generation), it must finish distribution of
the current generation events before starting distribution of the next
generation events.

<rdt>Why would this Consumer implementation choice be any more valid than a choice to queue pending events for each portlet and send them whenever a portlet is not actively processing events? In particular, why should the messaging protocol (WSRP) select what is a valid implementation choice for either of its endpoints (as opposed to defining the semantics of the message flow)? In the case of handleEvents, the semantics are the Consumer passing a set of events it chose to distribute to the Portlet. I think how the Consumer made the choice to distribute these particular events or chose to order the events should remain a Consumer choice.</rdt>

<YT>I think leaving the order to be the consumer is under-specifying. Let’s say that during the portlet’s run, it generated two events “Lakers” and “Pistons”. We require the portlet to return them in the correct order (in section, but we don’t specify that the consumer need to send these events to another portlet in the correct order, which means whether it will display Lakers or Pistons is completely random.

I think the order SHOULD be kept by the consumer, or at least we need to make such a recommendation. Of course, we are not even requiring the consumer to propagate the events, so there is no place for a MUST here. This does not necessarily imply the concept of generations, which is a simplification of the ordering requirement.</YT>  

2.                 What to do when handleEvent() returns redirectUrl? Should the
Consumer redirect immediately, or should it finish the event
distribution first? What if different Portlets handling the same event
return different redirectUrls?
Or may be the Consumer should ignore the redirectUrls of the event
handling, and respect only the result of the blocking action which has
triggered the event chain?

<rdt> Consensus from previous discussions have been to leave this up to Consumer policy. Spec should probably explicitly state this.</rdt>

3.                 The optimization when a Portlet sends markup in the
UpdateResponse seems a bit problematic, because the same Portlet may be
invoked several times within the same "three-step" loop generating each
time a different markup...

<rdt>Remember that each time a Portlet returns markup, it is saying this markup reflects its current state. Unless the Portlet changes its navState, mode or ..., the previously returned markup may be fetched from a cache.</rdt>

Considering all these complications I would propose to redesign the
HandleEventResponse so that it will include neither redirectUrl, nor
Events. This would make the event handling flow more simple and
As for the "cascading multi-generation events" (which will not be
supported in this case), they have so many side effects that could
easily cause unpredictable behavior.

<rdt>But they are also essential for a number of use cases. The only problems I have seen to-date with multiple generations is when people try to make this loosely-coupled model exhibit tightly-coupled behavior.</rdt>
<YT>I agree, but like some of the other questions raised recently around these topics, these are things that took us some serious discussions to realize. I think we need to add more wordage to the spec to explain the reasoning behind the decisions, and the expected use patterns. Otherwise we are going to get the same questions from everybody who reads the spec and was not part of the discussions…</YT>


-----Original Message-----
From: Subbu Allamaraju [mailto:subbu@bea.com]
Sent: Monday, March 07, 2005 7:29 PM
To: wsrp@lists.oasis-open.org
Subject: Re: [wsrp] spec-2.0-draft-05: events and blocking actions

Some more comments below.


>  From the Producer point of view, handling the user interactions and
> events are very similar tasks. The spec describes an interaction as an

> "encodable event" (6.4.2), which points out that interactions and
> are just two different ways to invoke the same Portlet logic.
> This idea however is not expressed strongly in the spec, which causes
> some confusion. Below is a list of questions:
> 1.        HandleEventResponse and BlockingInteractionResponse are
> identical, but defined as two distinct types, why is this?
> <rdt>Opened issue #43</rdt>

I thought we discussed this during last F2F, but I don't recollect what
the resolution was.

> 2.        According to paragraph Event Handling, the Consumer
> may invoke handleEvent() on different Portlets simultaneously. But if
> the event handling has the same Producer-side semantics as processing
> user interaction, all the restrictions described in paragraph 6.4.1
> be applicable as well. Which means that all the operations on the page

> must be blocked until handleEvent() either returns or fails.
> <rdt>My understanding from the discussion to-date is that handleEvent
> invocations may happen in parallel, but that other processing is
> until the Consumer decides it has no more events for a particular
> portlet. The Consumer may then start a getMarkup on that portlet. I'm
> sure we need to be more explicit about this ... do people think that
> Consumer must wait for all portlets to exit the event distribution
> before starting to collect markup? </rdt>

I agree that we need to be explicit. Semantically, it would be
consistent to specify that event distribution is blocking.

> 3.        What if HandleEventResponse contains events? Must they be
> processed by the Consumer?
> Let's consider a Consumer processing a page which contains two
> P1 and P2.
> a.        Consumer calls P1.performBlockingInteraction(), and gets
event E1
> b.        Consumer propagates the event to the Portlets:
>                                                                i.    
>  Question: should the consumer invoke P1.handleEvent(E1)? I guess
> <rdt>The Consumer is not bound to send the event to any portlets and I

> expect most will explicitly exclude the source portlet. Should we make

> this explicit in the spec so that portlets design for it?</rdt>

It is perfectly valid for P1 to subcribe for E1. I don't see any reason
to exclude this possibility.
>  Consumer calls P2.handleEvent(E1) and gets another event E2 in the
> response.
>                                                             iii.    
>  Must the Consumer call P1.handleEvent(E2)? If yes, there could be an
> endless loop; if no, the HandleEventResponse should not contain
> <rdt>The Consumer is free to exit the event distribution step whenever

> it wants to. As part of loop prevention, Consumers should have a limit

> on the number of generations of events they distribute ...</rdt>
> Regards,
> Artem
> *Artem Spector* | Portal Platform Infrastructure | NetWeaver
> Platform | SAP Labs Israel| (+972-9) 7779567

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