[jira] [Created] (KAFKA-7985) Cleanup AssignedTasks / AbstractTask logic

["Guozhang Wang (JIRA)" <ji...@apache.org>]

Guozhang Wang created KAFKA-7985:
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             Summary: Cleanup AssignedTasks / AbstractTask logic
                 Key: KAFKA-7985
                 URL: https://issues.apache.org/jira/browse/KAFKA-7985
             Project: Kafka
          Issue Type: Improvement
            Reporter: Guozhang Wang


Today the life time of a task is:

created -> [initializeStateStores] -> 
restoring (writes to the initialized state stores) -> [initializeTopology] -> 
running -> [closeTopology] -> 
suspended -> [closeStateManager] -> 
dead

And hence the assigned tasks contains the following non-overlapping sets : created, restoring, running, suspended, (dead tasks do no need to be maintained). Normally `created` should be empty since once a task is created it should move on transit to either restoring or running immediately. So whenever we are suspending tasks, we should go through these sets and act accordingly:

1. `created` and `suspended`: just check these two sets are always empty.
2. `running`: transit to `suspended`.
3. `restoring`: transite to `suspended`. But the difference here is that we do not need to close topology since it was not created yet at all; we just need to remember the restored position, and keep the restorers on hold instead of clearing all of them.



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