ifndef-SleePy opened a new pull request #11347: [FLINK-14971][checkpointing] Make all the non-IO operations in CheckpointCoordinator single-threaded URL: https://github.com/apache/flink/pull/11347 ## What is the purpose of the change * This is the last part of refactoring threading model of `CheckpointCoordinator` * The threading model of `CheckpointCoordinator` would be simplified a lot * All the non-IO operations are executed in a single-threaded way * A lot of competitions inside or outside `CheckpointCoordinator` could be avoided. So it's easier for `CheckpointCoordinator` to cooperate with other components ## Brief change log * Split the ACK and declined message handling into two ways * Handle non-IO operations in timer thread * Handle IO operations in IO thread * This is a preparation of introducing main thread executor in `CheckpointCoordinator`. After this, there would be non-IO operations executed in IO thread * Introduce main thread executor in `CheckpointCoordinator` * It's used to execute all non-IO operations instead of the timer thread now * The timer thread would be kept for now. It's only used to schedule the periodic triggering, because currently main thread executor does not support periodic scheduling yet. * The coordinator-wide lock of `CheckpointCoordinator` and lock of `PendingCheckpoint` could be avoided because there is no thread competition after introducing main thread executor ## Verifying this change * This change is already covered by existing tests, and some test cases are added at the same time ## Does this pull request potentially affect one of the following parts: - Dependencies (does it add or upgrade a dependency): no - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: no - The serializers: no - The runtime per-record code paths (performance sensitive): no - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: no - The S3 file system connector: no ## Documentation - Does this pull request introduce a new feature? no - If yes, how is the feature documented? not applicable
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