[FLINK-13059][Cassandra Connector] Release Semaphore correctly on Exception in send()

[mchro]

What is the purpose of the change

Release the MaxConcurrentRequests Semaphore correctly, if an exception happens in send(). This should make flush() not deadlock, but just in case: make flush timeout controllable by MaxConcurrentRequestsTimeout.

Brief change log

• Release Semaphore correctly on Exception in send()
• Use getMaxConcurrentRequestsTimeout() also for flush

Verifying this change

This change added tests and can be verified as follows:

• Added unit test that validates semaphore released if Exception in send(); test fails before change.

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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Automated Checks

Last check on commit 811a803 (Fri Sep 06 09:08:52 UTC 2019)

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[klion26]

thanks for your contribution, could you please rebase the latest master and let the Travis build passed?

[zentol]

CI report for commit 18b9bf2: FAILURE Travis

[flinkbot]

CI report for commit 7fe8595: SUCCESS Build

[mchro]

I rebased on master, and the Travis build seem to have passed (even though Github is still indicating checks failed). Let me know if I should do anything additional.

[flinkbot]

CI report:

• 7fe8595 : FAILURE Build
• 811a803 : FAILURE Build

[klion26]

thanks for the rebasing, I just left a little comment.
Currently, we rely on the build status update by @flinkbot

[klion26]

Do you think we should refactor the tryAcquire() function to tryAcquire(int permits) so that we can reuse it here?

[mchro]

Yes, good idea. I will push an additional commit with this refactor.

[klion26]

As this function is private, do we still need to keep it? or just call tryAcquire(int permits) directly in invoke

[mchro]

Guess it is a matter of style; I removed the overloaded function, and just call tryAcquire(1)

[klion26]

LGTM now, we need to wait for some committer for a final pass.