XComp opened a new pull request, #20709:
URL: https://github.com/apache/flink/pull/20709
## What is the purpose of the change
CURATOR-645 covers a bug in the LeaderLatch implementation that causes a
race condition if a child node, participating in the leader election, is
removed too fast. This results in a different code branch being executed which
triggers a reset of the LeaderLatch instead of re-collecting the children to
determine the next leader.
The issue occurs because LeaderLatch#checkLeadership is not executed
transactionally, i.e. retrieving the children and setting up the watcher for
the predecessor is not done atomically. This leads to the race condition where
a children (the previous leader's node) is removed before setting up the
watcher which results in an invalid handling of the situation using reset.
Adding some sleep here (simulating the leader actually doing something) will
reduce the risk of falling into the race condition because it will give curator
to more time to set up the watchers properly. This is only meant as a temporary
solution until CURATOR-645 is resolved and the curator dependency on the Flink
side is upgraded.
## Brief change log
* Adds a minor `Thread.sleep` to simulate actual workload on the leader to
prevent the LeaderLatch going into the buggy code branch.
## Verifying this change
Runs test repeatedly without the fix and with the fix to see whether we can
observe a difference.
## 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, 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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