I'm looking for some good library for processing tasks (or 'operations' as we call them in our domain model) for Java or .NET. We save each operation to perform in db and then we need some mechanism for fetching unprocessed tasks from db, process them and update db record with proper status ('processed OK' / 'process error').
The trick is that operation can depend one on another. For example when 'Operation Payment' is being processed the system might discover that we need to perform 'Operation Check Payment Data' before - so it should create new operation row in db, pause performing 'Operation Payment', process 'Operation Check Payment Data' in next turn and after it completes go back to processing 'Operation Payment'.
I'll show you how we manage this at the moment.
We've got db table 'operations'. Cron-like mechanism runs each minute and fetches first 100 unprocessed operations from db and process it. If (while processing) system finds that some other operation (B) is needed to perform current operation (A), then new operation (B) record is created and performing current operation (A) is halted. Next minute cron fetches operations A and B. Operation A is fetches as it is not processed but system sees that dependent operation B is already created so it does not create it once again. Operation B is processed and status 'processed OK' is saved in proper row in db. Next minute cron fetches operation A from db and can finally perform it because dependent task is completed.
We are looking for ways to make it simpler, better and more elegant.