[FLINK-13469][state] Ensure resource used by StateMapSnapshot will be released if snapshot fails

[banmoy]

What is the purpose of the change

Currently, resource used by StateMapSnapshot may not be released by StateTableSnapshot if snapshot fails. For example, If exception happens in StateMapSnapshot#writeState, resources used by current and left StateMapSnapshot can not be released. This PR will fix this problem.

Brief change log

• make sure all resources are released in StateTableSnapshot#release()
  • CopyOnWriteStateTableSnapshot will check whether the resource is released for each CopyOnWriteStateMapSnapshot in CopyOnWriteStateTableSnapshot#release(), and release them if not
  • NestedMapsStateTableSnapshot need do nothing in NestedMapsStateTableSnapshot#release(). On the one hand, nested snapshot is synchronous, and doesn't hold all state map snapshots which will be used in async part like copy-on-write snapshot. State map snapshot for a key-group will not be created until it's turn to write state of this key group, so there is no resource to need to release except for current state map snapshot. On the other hand, nested state map snapshot actually hold no resource. So NestedMapsStateTableSnapshot need do nothing for release.
• remove default implementation AbstractStateTableSnapshot#release(). The reasons are as follows:
  • the way to release for the copy-on-write and the nested is very different, so there is no much meaning to provide default implementation
  • force subclass to think about the proper way to release, and make it more safety

Verifying this change

This change added tests and can be verified as follows:

• Added test CopyOnWriteStateTableTest#testReleaseForSuccessfulSnapshot and CopyOnWriteStateTableTest#testReleaseForFailedSnapshot to validates that resources can be released no matter snapshot is successful or failed

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, 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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Last check on commit 4487019 (Wed Dec 04 14:59:52 UTC 2019)

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CI report:

• dae038f : FAILURE Build
• d2cc6e9 : SUCCESS Build
• 1aaf61a : FAILURE Build
• 0643fce : FAILURE Build
• 6b42e10 : FAILURE Build
• 4487019 : SUCCESS Build

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[banmoy]

The failed test is KafkaProducerExactlyOnceITCase.testExactlyOnceCustomOperator which does not use keyed state, so it seems irrelevant to this PR. And FLINK-13527 has been created to track this issue. Retrigger the CI.

[banmoy]

@flinkbot run travis