Title: [wsbpel] Issue 274 Proposal to Vote
Alex,
I
agree with your first point in that this is a modeling error or unanticipated
runtime failure.
I
am not in complete agreement with the second. The compensation handler is an
optional continuation of the scope but the scope is in a different state during
its compensation so it's not so strange to me to have different rules for
checking for error conditions. Since the scope's fault handlers have been
uninstalled then I consider it the responsibility for an activity outside
of the scope to detect the fault.
I
don't agree with your third point. I view the faults in bpel as being raised as
soon as they are detected by the engine. This detection process occurs through
the execution of an activity, evaluation of a link, receipt of data ...etc. In
the case of bpel:missingReply, there is no fault until the check is made. The
previous four bullets in this section have normative language about when the
check for the orphaned IMA's is made, not how the fault is
handled.
That said, I think your most compelling argument
for having the CH check for the orphaned IMA's is that the compensation work for
multiple scopes may be related so you would want the compensation handler to
check for orphaned IMA's fault immediately. On the other hand, they may not be
related so it could be better to let it continue.
Lastly, the syntax below for providing <catchAll>
around the <compensateScope> only allows continuation for other targets
and not other instances within the same instance group. Granted, the language
for faults within an instance group cause it to short circuit but I go back to
my point above about the difference between a fault and the check for the
condition.
In any case, we need to close this issue on the next
call so I'd appreciate any additional feedback or other input from the
group.
Thanks.
From: Alex Yiu [mailto:]
Sent: Wednesday, May 10, 2006 4:26 PM
To: Mark
Ford
Cc: ; Alex Yiu; Danny van der Rijn;
'Dieter Koenig1'
Subject: Re: [wsbpel] Issue - 274 - Proposal to
Vote
Hi Mark,
I guess you would not be surprised
that I still prefer detecting orphaned IMA at the end of compensationHandler.
Reasons are:
The missingReplies error is actually resulted from the modelling mistake
or unanticipated runtime failure in the child scope (which the CH is
attached), not the FH of the parent scope. Fault at the CH level is more
precise.
From section 12.4.2: "This is
because their compensation handlers are still available, and therefore the
execution of such scopes may continue during the execution of their
compensation handlers, which can be thought of as an optional
continuation of the behavior of the associated scope." I tend to
interprete that the primary (normal) activity of the scope is its part #1,
while the activity of the CH of that scope is its part #2. Their nature should
be symmetrical in the counter-working way. If we perform certain checks in
part #1, similar checks should happen in part #2.
The asymmetry between missingReplies and other fault (e.g.
selectionFailure) concerns me. (This is the last but the most important
point.) If there is a problem in the CH logic that triggers a fault (e.g.
selectionFailure), it will be propagated from the CH to the corresponding
compensation activity in FCTHandler (fault, compensation and
termination). If there is no fault handling around the compensation
activity, the whole FCTHandler will not continue. But, now we are saying that
the FCTHandler will continue until its end, if the error condition is the
missingReplies fault? This asymmetry may be surprising to users. I would say
it may the process more difficult to model.
Let me use one
more example to illustrate my preference. If one wants to continue the logic in
a FH including continuing other compensation activities, one want to add a
scope
That is changing
from:
---------------------------------------
<catch ...
>
<sequence>
<compensationScope target="A"
/>
<compensationScope
target="B" />
<compensationScope target="C" />
</sequence>
</catch>
---------------------------------------
to:
---------------------------------------
<catch ...
>
<sequence>
<scope>
...
<catchAll> <empty/>
</catchAll>
...
<compensationScope target="A" />
</scope>
<compensationScope target="B"
/>
<compensationScope
target="C" />
</sequence>
</catch>
---------------------------------------
This <catchAll> will
handle all kind of faults, not just missingReplies.
Again, it will allow
BPEL process definition to have a finer grain of control on how to handle
missingReplies fault.
Also, **if** the work of "A", "B" and "C"
are highly related to each other, I would say that it is actually more common
for the process designer to prefer the compensation work stop immediately, if
the compensation of "A" failed. That will avoid any propagating any strange
states from "A" to "B" and "C". That is also consistent with the design of
Compensation Handler Instance Group. That is, if one instance fails within the
group, other instances (not started yet) will not be attempted.
I
hope I did a better convincing job this time. :-)
More thoughts?
Thanks!
Regards,
Alex Yiu
Mark Ford wrote:
In dealing with an orphaned IMA within a
compensation handler, it seems to me that there are two possible resolutions.
Either the compensation handler detects the orphaned IMA's and faults or the
detection of orphaned IMA's is deferred to the fault handler or termination
handler that invoked the compensation handler. I am in favor of the latter
since it allows compensation to continue even with orphaned IMA's. There is
very little that can be done with these orphaned IMA's so we may as well allow
the compensation logic to proceed as best it can and defer its fault to
I have reworded my original proposal to avoid
introducing any new terms as per Danny's suggestion. The approach is still the
same in that the detection of an orphaned IMA is NOT made by the
compensationHandler.
Add a fifth bullet to Section 12.2 which reads as
follows:
No checks for orphaned IMA's are made when
a compensation handler completes. The compensation handler's execution must
necessarily start from within a fault or termination handler so any orphaned
IMA's created by a compensation handler will be detected and handled as
described in the above bullets.
