[FLINK-24538][runtime][tests] Fix ZooKeeperLeaderElectionTest.testLeaderShouldBeCorrectedWhenOverwritten fails with NPE

[xmarker]

What is the purpose of the change

Fix ZooKeeperLeaderElectionTest.testLeaderShouldBeCorrectedWhenOverwritten fails with NPE

Brief change log

• Use a local function variable to store the value polled from leaderEventQueue in CommonTestUtils.waitUntilCondition lambda in case instance field changes

Verifying this change

(Please pick either of the following options)

This change added tests and can be verified as follows:

• Use old ZooKeeperLeaderElectionTest.testLeaderShouldBeCorrectedWhenOverwritten unit test

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, Kubernetes/Yarn, 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)

[flinkbot]

Thanks a lot for your contribution to the Apache Flink project. I'm the @flinkbot. I help the community
to review your pull request. We will use this comment to track the progress of the review.

Automated Checks

Last check on commit 8b1933c (Fri Oct 15 16:22:55 UTC 2021)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!
• This pull request references an unassigned Jira ticket. According to the code contribution guide, tickets need to be assigned before starting with the implementation work.

_{Mention the bot in a comment to re-run the automated checks.}

Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

Please see the Pull Request Review Guide for a full explanation of the review process.

The Bot is tracking the review progress through labels. Labels are applied according to the order of the review items. For consensus, approval by a Flink committer of PMC member is required

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot approve description to approve one or more aspects (aspects: description, consensus, architecture and quality)
• @flinkbot approve all to approve all aspects
• @flinkbot approve-until architecture to approve everything until architecture
• @flinkbot attention @username1 [@username2 ..] to require somebody's attention
• @flinkbot disapprove architecture to remove an approval you gave earlier

[flinkbot]

CI report:

• 8b1933c Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[dmvk]

Thanks for the PR @xmarker. Sorry this haven't been reviewed earlier. My biggest concern is that the PR doesn't seem to cover all scenarios (eg. waitForEmptyLeaderInformation is still prone to the same race condition).

The main problem is in a race condition, where the leader property is being assigned by multiple threads without synchronization. There already seems to be the proper mechanics in place to solve this using blocking queues.

I'm wondering, could the fix be as simple as the snippet bellow?

diff --git a/flink-runtime/src/test/java/org/apache/flink/runtime/leaderelection/TestingRetrievalBase.java b/flink-runtime/src/test/java/org/apache/flink/runtime/leaderelection/TestingRetrievalBase.java
index f32440199bb..02b131da5a7 100644
--- a/flink-runtime/src/test/java/org/apache/flink/runtime/leaderelection/TestingRetrievalBase.java
+++ b/flink-runtime/src/test/java/org/apache/flink/runtime/leaderelection/TestingRetrievalBase.java
@@ -118,7 +118,6 @@ public class TestingRetrievalBase {
 
     public void offerToLeaderQueue(LeaderInformation leaderInformation) {
         leaderEventQueue.offer(leaderInformation);
-        this.leader = leaderInformation;
     }
 
     public int getLeaderEventQueueSize() {

[dmvk]

cc @wangyang0918

[wangyang0918]

Sorry for the late response. @dmvk I think your suggestion makes sense to me. Then we will have only one place waitForNewLeader or waitForEmptyLeaderInformation to update the leader.

@xmarker WDYT?

[XComp]

Closing this PR in favor of PR #19041