[jira] [Created] (FLINK-6684) Remove AsyncCheckpointRunnable from StreamTask

["Stefan Richter (JIRA)" <ji...@apache.org>]

Stefan Richter created FLINK-6684:
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             Summary: Remove AsyncCheckpointRunnable from StreamTask
                 Key: FLINK-6684
                 URL: https://issues.apache.org/jira/browse/FLINK-6684
             Project: Flink
          Issue Type: Improvement
          Components: State Backends, Checkpointing
            Reporter: Stefan Richter


Right now, {{StreamTask}} executes {{AsyncCheckpointRunnable}} to run the async part of a snapshot. However, it seems that currently the main reason for executing this code in a separate tread is to avoid its execution under the checkpoint lock, so that processing can proceed.

Actually, the  checkpoint is already triggered asynchronously, in {{Task::triggerCheckpointBarrier}}. We could also execute the checkpointing without executing {{AsyncCheckpointRunnable}}, by just running the code inside the thread that is spawned in {{Task::triggerCheckpointBarrier}}. We could simply

1) Run the synchronous part of the checkpoint under the checkpointing lock.
2) Run the asynchronous part of the checkpoint without holding the checkpointing lock.
3) Returning a {{Future}} from {{StatefulTask::triggerCheckpoint}} when called from {{Task::triggerCheckpointBarrier}}.

This would simplify the code and make the usage of the {{SafetyNetCloseableRegistry}} possible as intended. 



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