Yaron,
May be we should instead forbid the name of the variable in getVariableData
to be dynamic. It seems that this idea was raised in the F2F. I think that
this is a path we should explore.
Edwin
> -----Original Message-----
> From: Yaron Goland [mailto:]
> Sent: Wednesday, October 08, 2003 3:17 PM
> To: 'Satish Thatte';
> Subject: RE: [wsbpel] Issue 3 -- proposal for discussion
>
> That's it! Thank you. When I wrote up the letter something
> was really bugging me but I couldn't figure out what it was
> and so eventually just sent the letter. Your letter reminded
> me what was bugging me.
>
> Since one can use getVariableData functions whose
> variableName is itself a variable one must use annotations
> otherwise one has to persist all values.
>
> So the answer to the last question in my letter is - No,
> static analysis cannot always determine when a compensation
> handler has accessed a variable that has not been marked for
> 'freezing'. Instead we will have to have runtime checking
> that can throw a fault if a getVariableData function should
> have a variableName argument whose value does not resolve to
> a 'frozen' or 'live' value.
>
> Yaron
>
>
>
> > -----Original Message-----
> > From: Satish Thatte [mailto:]
> > Sent: Wednesday, October 08, 2003 1:26 PM
> > To: ;
> > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion
> >
> >
> > Yaron,
> >
> > It should be fairly straightforward to detect which non-local
> > variables are actually used in compensation handlers and
> persist only
> > those. What you are suggesting is an extra annotation that allows
> > additional verification of intent via redundancy. Seems OK
> though a
> > bit onerous, and nothing at all to do with cost. Do other
> people have
> > opinions?
> >
> > The bigger issue for cost is detecting when a scope snapshot is no
> > longer needed because there is no "path" left to invoke it.
> In other
> > words, snapshot GC.
> >
> > Satish
> >
> > -----Original Message-----
> > From: Yaron Goland [mailto:]
> > Sent: Wednesday, October 08, 2003 1:10 PM
> > To: Satish Thatte;
> > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion
> >
> > Is one of the practical consequences of proposal 2 that all scope
> > variables must be persisted when the scope successfully completes if
> > either:
> > A) The scope has a non-default compensation handler or
> > B) The scope's variables are 'visible' from a scope with a
> > non-default compensation handler (e.g. imagine if S1 and S3 had
> > compensation handlers but S2 just had a default
> compensation handler.
> > In that case S2 would still need to persist its variables
> since they
> > would be 'visible' from S3)?
> >
> > Doesn't this seem a bit expensive? BPEL processes can run
> for months
> > or even years, building up lots of scopes all of whose
> variables would
> > have to be persisted.
> >
> > Might it not be more economical to include an attribute that can be
> > included on variable declarations to define which variables
> should be
> > available for use by compensation handlers?
> >
> > Couldn't static analysis then catch cases where a
> compensation handler
> > attempts to access a variable which has not been marked as being
> > available for compensation handlers?
> >
> > Thanks,
> >
> > Yaron
> >
> > > -----Original Message-----
> > > From: Satish Thatte [mailto:]
> > > Sent: Wednesday, October 08, 2003 7:07 AM
> > > To:
> > > Subject: RE: [wsbpel] Issue 3 -- proposal for discussion
> > >
> > >
> > > One more time - this time with a more accessible JPEG
> > picture courtesy
> > > of Sid Askary.
> > >
> > > Better formatted version of the same mail ..
> > >
> > > BPEL currently specifies that a compensation handler lives in a
> > > snapshot world in which the state of the associated scope and all
> > > enclosing scopes has been preserved as it was when the associated
> > > scope completed.
> > > There is an outstanding BPEL issue (Issue#3) that points out that
> > > there is a need for compensation handlers to affect and
> be affected
> > > by the "current state of the world".
> > >
> > > Proposal #1: The proposal on the table has been to add
> inbound and
> > > outbound parameters to compensation handlers to allow invokers of
> > > compensation to send data into and get data out of the
> compensation
> > > process.
> > >
> > > Proposal #2: Choreology put an alternative proposal on the table.
> > > Restated, it basically says that compensation handlers
> > always see the
> > > current state of the world. The current state of the world for
> > > completed scopes is their state as it was at the time of
> completion.
> > > They are in suspended animation because their
> compensation handlers
> > > are still alive and therefore their execution may "continue" in
> > > compensation mode. Thus for enclosing scopes the compensation
> > > handler
> > either sees
> > > live state (if the scope is not completed) or the state
> of the scope
> > > as it was when that scope completed.
> > >
> > > In the attached picture showing three nested scopes S1,
> S2 and S3,
> > > their compensation handlers C1, C2, C3, and failure
> handlers F1 and
> > > F2, we may have an error handling call stack F1->C2->C3. In that
> > > case
> > > C3 will see
> > > the state of S2 as it was when S2 completed. However
> that is also
> > > what
> > > C2 is seeing and C2 has called C3, therefore there is a
> > consistency of
> > > visible state in the call stack.
> > >
> > > The positives and negatives of these two proposals mirror each
> > > other. A positive aspect of the second proposal is that
> parameters
> > > are not needed for data flow to and from live state to
> compensation
> > > handlers, and compensation handlers with live state
> contact can be
> > > used in default compensation, unlike the first proposal. The
> > > negative
> > aspect is that
> > > compensation handlers will now participate in concurrency control
> > > issues relating to live state, and will need to use serializable
> > scopes when
> > > they touch non-local state, again unlike the first proposal. The
> > > concurrency control problem also has an impact on Issue#10
> > which deals
> > > with serialization of compensation handlers.
> > >
> > > On the whole, given the alternatives, the second alternative is
> > > preferable, especially because it maintains default compensation
> > > semantics. I propose to resolve Issue 3 along the lines of the
> > > Proposal #2.
> > >
> > > Satish
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
>
