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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