Help identify the pattern for reacting on updates
- by Mike
There's an entity that gets updated from external sources. Update events are at random intervals. And the entity has to be processed once updated. Multiple updates may be multiplexed. In other words there's a need for the most current state of entity to be processed.
There's a point of no-return during processing where the current state (and the state is consistent i.e. no partial update is made) of entity is saved somewhere else and processing goes on independently of any arriving updates.
Every consequent set of updates has to trigger processing i.e. system should not forget about updates. And for each entity there should be no more than one running processing (before the point of no-return) i.e. the entity state should not be processed more than once.
So what I'm looking for is a pattern to cancel current processing before the point of no return or abandon processing results if an update arrives. The main challenge is to minimize race conditions and maintain integrity.
The entity sits mainly in database with some files on disk. And the system is in .NET with web-services and message queues.
What comes to my mind is a database queue-like table. An arriving update inserts row in that table and the processing is launched. The processing gathers necessary data before the point of no-return and once it reaches this barrier it looks into the queue table and checks whether there're more recent updates for the entity. If there are new updates the processing simply shuts down and its data is discarded. Otherwise the processing data is persisted and it goes beyond the point of no-return.
Though it looks like a solution to me it is not quite elegant and I believe this scenario may be supported by some sort of middleware.
If I would use message queues for this then there's a need to access the queue API in the point of no-return to check for the existence of new messages. And this approach also lacks elegance.
Is there a name for this pattern and an existing solution?
