[bt-spec] When to garbage collect cohesions?

[Mark Little <mark_little@hp.com>]

Given that we allow prepare_inferiors and cancel_inferiors to be called many times during the lifetime of a cohesion, this raises an interesting garbage collection problem: when is a cohesion finished? If I send confirm_transaction then the answer is easy. However, consider the case where prepare_inferiors(all) indicates they all cancelled or resigned, or cancel_inferiors(all) says likewise, is the cohesion finished? The answer is "perhaps", or "it depends", since surely I may expect new inferiors to be enlistable later? But maybe I don't! Perhaps I do want the cohesion to terminate?

 

Solution? Several:

 

(i) we mandate that every user of a cohesion must send confirm_transaction. Not my favourite option.

 

(ii) if prepare_inferiors(all) or cancel_inferiors(all) is used and they indicate all current inferiors have gone away, then the cohesion is finished. Again, not a great idea but it does cut down on an explicit "end cohesion" message.

 

(iii) add an explicit "end cohesion" message. Hmmm, see above.

 

(iv) we add a Qualifier that basically says do (ii) if the conditions are right. The default is don't.

 

Or maybe I've completely missed something in the spec that already covers this.

 

Mark.

 

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Dr. Mark Little, Distinguished Engineer,
Transactions Architect, HP Arjuna Labs
Email: mark_little@hp.com
Phone: +44 191 2606216
Fax  : +44 191 2606250