[FLINK-18163][task] Add RecordWriter.volatileFlusherException

[rkhachatryan]

What is the purpose of the change

RecordWriter.flusherException is updated by one thread and checked by another.
The field is deliberately non-volatile for performance reasons.
But this way exception can be never seen by the 2nd thread.

This PR adds an additional volatile field which is checked every N times.

Verifying this change

TBD: no tests added yet

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): yes
• 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? no

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Automated Checks

Last check on commit a47aa12 (Mon Jul 06 08:56:33 UTC 2020)

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• ❓ 1. The [description] looks good.
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• ❓ 3. Needs [attention] from.
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[flinkbot]

CI report:

• 43390e7 Azure: FAILURE

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[rkhachatryan]

CI build failure unrelated: https://issues.apache.org/jira/browse/FLINK-18485

[pnowojski]

LGTM % one suggestion (adding a comment). Is the test failure related?

[rkhachatryan]

No,

CI build failure unrelated: https://issues.apache.org/jira/browse/FLINK-18485

(2nd build is PENDING at the moment)

[pnowojski]

LGTM, could you squash the commits so I could merge it?

[rkhachatryan]

Done.