Re: [wsbpel] Issue 6.2 - What about compensation handlers?

[Alex Yiu <alex.yiu@oracle.com>]

Hi Yaron,

Assuming that we take Satish's interpretation that we allow a partial termination of a <scope>. That is, NOT forcing using <scope> within a <flow> with a completionCondition.

If I read the termination part of spec correctly and understand Satish's interpretation of the spec, the compensationHandlers under the while will NOT be lost. Let me put more words to illustrate what I expect:

--------------------------------
scope name="A"
    flow
       completionCondition ...
          ...
       while
          scope name="C"
             compensationHandler
                ...
             ...
       sequence name="done"
          ...
--------------------------------

Say the while loop execute from 1 to 10. During the execution of loop #4, the sequence of name "done" triggers the early completion condition. Hence, a termination happens to <while> loop.

The scope #1, #2, #3 (of name="C") got successfully executed. The compensationHandlers are installed for these 3 scopes. The scope #4 got terminated and its terminationHandler got triggered. Again, as we allow a partial termination, the compensationHandler of the first 3 scopes will remain untouched. They will be available to the scope-A to call, if needed in the compensationHandler or faultHandler of scope-A.

On the other hand, if one puts a scope-B around <while>-activity and within the <flow>. The termination/compensation will be different.

--------------------------------
scope name="A"
    flow
       completionCondition ...
          ...
       scope name="B"
           while
              scope name="C"
                 compensationHandler
                    ...
                 ...
       sequence name="done"
          ...
--------------------------------

The scope #1, #2, #3 (of name="C") got successfully executed. The compensationHandlers are installed for these 3 scopes.

After the completionCondition is triggered, whe whole scope-B is being terminated. The termination of scope-B will involve two parts:

• cascade the termination to scope #4 (Hence, its terminationHandler got triggered). 
  
• invoke the compensation handlers of scope #1, #2, #3.
  

In this case, the whole scope-B got terminated. So, the compensation handlers of scope #1, #2, #3 will NOT be available to the scope-A to call. Please note: this semantic has NOTHING to do with early completion logic. It just shows a scope works today.

I believe that once we incorporate Satish's interpretation and clarification about the possibility of a partial termination of a scope. Then, this proposal would provide crispy clear picture and foundation on how an early completion would work in BPEL. And, we should be ready to go for the formal voting.


Thanks!



Regards,
Alex Yiu


Yaron Y. Goland wrote:

Imagine the following sample code:

flow
   completionCondition ...
      ...
   while
      scope
         compensationHandler
            ...
         ...
   sequence name="done"
      ...

Now imagine that the "done" sequence completes triggering the completion condition and terminated the while. But the while had already completed a few iterations and instantiated a number of compensation handlers. What happens to those handlers?

Using the current termination language those handlers would be lost when the parent scope is terminated. I suspect most programmers would find this behavior to be surprising.

        Yaron


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