No where in the spec we say control dependency exists regardless of
joinCondition. So, we have scope for interpretation and so, things look
fine to you when they did not to me. We need to minimally correct that.
Let us look at what it really means for the control dependency to exist
regardless of the joinCondition. So I want to wait for all source
activities to complete (successfully or not) and I want to proceed only
if the join-condition evaluates to true when it is implicit join or OR
join on all links. That is fine but this is modeling a very special
case IMO, generally we don't wait for things to complete, the success
or failure status of which we don't care about. Even if one cared one
should perhaps capture that via an explicit AND joinCondition rather
than rely on an implicit syntactic sugar.
Where as more simpler (perhaps common) case would be to wait on any one
(or n < total) of the source activities to complete successfully
(like a barrier in threads). How can one model that?
It seems we have an issue here.
Regards, Prasad
Danny van der Rijn wrote:
Things
look fine to me. For (2) and (3), you have to realize that a
control dependency exists regardless of the joinCondiiton. If you
don't want the control dependency, don't draw a link. (4) is referring
to an explicit piece of code (the Initial Example) in which your
stipulation ("...is only one of
the incoming links...") is not correct, since there is only one link
target.
Danny
Prasad Yendluri wrote:
Hi,
We have the following text dispersed in sections 12.5.1 and 12.5.2 that
results in an inconsistent specification of evaluation of Link Join
conditions. The spec states:
(1) Section 2.5.1: Every activity that is
the target of a link has an implicit or explicit “join condition”
associated
with it. If the explicit join
condition is missing, the implicit condition requires the status of "at least one" incoming link to be positive (see below for
an explanation of link status).
So, the implicit join is an "OR" and the join condition evaluates to
true as soon as the status of one of the incoming links to the activity
is positive.
(2) Section 2.5.1: If an activity that is
ready to start in this sense has incoming links, then it does not start
until
the status of "all" its incoming links has been determined and the (implicit
or
explicit) join condition associated with the activity has been
evaluated.
If it is an implicit join why should the activity not start as soon as
one (or more) of its incoming links goes to a positive? Why should it
wait until the status of all incoming activities has been determined?
(3) Section 2.5.1: For
each
activity B that has a synchronization dependency on A, check whether:
o
B is ready
to start (except for its dependency on incoming links) in the sense
described
above.
o
The status
of all incoming links for B has been determined.
Again why the requirement to wait until the status of all incoming
activities is determined?
(4) Section 12.5.2: If one of
these invocations were
to fault, the status of the outgoing link from the invocation would be
negative, and the (implicit) join condition at the target of the
link would be
false, but the resulting bpws:joinFailure would be implicitly suppressed and the
target activity would be silently skipped within the sequence instead
of
causing the expected fault.
If the link that was set to false (due to the failure) is only one of
the incoming links to an "implicit join", shouldn't the join condition
evaluate to false only when all other links to the join also evaluate
to false.
It seems either the parts related implicit join in (2),(3),(4) above or
incorrect or (1) itself was not correct. I believe 1 is correct.
Either way it seems we need to fix this. Comments?
Regards, Prasad
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