sorter: fix Unified Sorter error handling & add more unit test cases (#1619)

[ti-srebot]

cherry-pick #1619 to release-5.0
You can switch your code base to this Pull Request by using git-extras:

# In ticdc repo:
git pr https://github.com/pingcap/ticdc/pull/1678

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/ticdc.git pr/1678:release-5.0-22774319c392

---

What problem does this PR solve?

• Unified Sorter might return an unhelpful error ErrWorkerPoolHandleCancelled for some IO errors.
• Some error handling code might cause data race.

What is changed and how it works?

• Filter the ErrWorkerPoolHandleCancelled error.
• Add appropriate synchronization to avoid races.
• Add unit test cases for these fixes.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix Unified Sorter returning unhelpful error messages & other misc. fixes.

[ti-srebot]

/run-all-tests

[zier-one]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• leoppro

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 writing /lgtm in a comment.
Reviewer can cancel approval by writing /lgtm cancel in a comment.

[zier-one]

/merge

[ti-chi-bot]

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

Commit hash: 85aedf5

[liuzix]

/run-all-tests tikv=pr/9987

[zier-one]

/run-all-tests tikv=pr/9987

[amyangfei]

/run-all-tests

[zier-one]

/rebuild

[liuzix]

/merge

[ti-chi-bot]

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

Commit hash: 56f70fd

[liuzix]

/run-all-tests

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.