[FLINK-12101] Race condition when concurrently running uploaded jars via REST

[leesf]

What is the purpose of the change

Fix race condition when concurrently running uploaded jars via REST.

Brief change log

• Introduce a ThreadLocal field to store ExecutionEnvironmentFactory
• When contextEnvironmentFactory is null, use ThreadLocal to get Factory.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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 documented)

cc @tillrohrmann

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[klion26]

Do we need to add contextEnvironmentFactoryThreadLocal check in the function areExplicitEnvironmentsAllowed(line 1284). I can't add a review there.

[leesf]

Thanks for your review @klion26. Good catch and updated.

[tillrohrmann]

Thanks for creating this PR @leesf. I had a comment about the precedence of the factory fields. Moreover, I think we need to do the same for the StreamExecutionEnvironment if I'm not mistaken.

It would also be good if we could add a test for this fix. We could create a dummy ExecutionEnvironmentFactory for this purpose.

[tillrohrmann]

I would suggest to first check the thread local variable and then fall back to the static variable. That way, it would not be possible to override the value of an ExecutionEnvironment which has been set explicitly by from another thread.

[leesf]

@tillrohrmann Thanks for your review. Updated this PR to address your comments.

[tillrohrmann]

Thanks for addressing my comments @leesf. LGTM. The failing test case is unrelated. Merging this PR now.