pkg/workerpool(cdc): fix race between handling error and unregistering handler (#4605)

[ti-chi-bot]

This is an automated cherry-pick of #4605

What problem does this PR solve?

Issue Number: close #4447

What is changed and how it works?

• Fixed race between handling error and unregistering handler in pkg/workerpool. The root cause is that, if an error has already caused a handler to be automatically unregistered, Unregister() will return immediately, regardless of whether the error handler has returned. This has caused race in unified sorter.

Check List

Tests

• Unit test
• Integration test

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch

Release note

Fix stability problem in workerpool, which is used by Unified Sorter.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[liuzix]

/run-integration-tests

[liuzix]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 5398795

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.3@d0e603b). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             release-5.3      #4682   +/-   ##
================================================
  Coverage               ?   55.6407%           
================================================
  Files                  ?        224           
  Lines                  ?      23880           
  Branches               ?          0           
================================================
  Hits                   ?      13287           
  Misses                 ?       9264           
  Partials               ?       1329