[FLINK-16383][task] Do not relay notifyCheckpointComplete to closed operators

[AHeise]

What is the purpose of the change

Through StreamOperatorWrapper an operator may already be closed while the StreamTask is still running. Notification might be relayed in that time from the task to the closed operator causing issues on operators reacting on completed checkpoints, such as two phase commit sinks.

Brief change log

• This commit adds the information of the closing to the wrapper and avoids relaying notifications to closed operators.
• Also fixes a potential related issue in SubtaskCheckpointCoordinatorImpl#takeSnapshotSync.

Verifying this change

• Added StreamTaskTest#testNotifyCheckpointOnClosedOperator

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Last check on commit 26b98ea (Fri Oct 16 10:50:44 UTC 2020)

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[pnowojski]

I wonder if we shouldn't throw some exception?

[AHeise]

It depends on what we are trying to achieve. Assume that we have a chain source -> map -> sink and source and map have been closed already. Wouldn't it be nice to still commit stuff in sink?

[pnowojski]

If one operator is closed in the chain, doesn't it mean all of them are closed?

[AHeise]

Not with the wrapper. It closes them one after another from head to tail with mails. That's why the notify can sneak in in the first place.
Only when one operator is closed completed, the next operator in line is closed.

[pnowojski]

LGTM % test failure?

[AHeise]

@flinkbot run azure