syncer(dm): fix the data race issue (#5881)

[ti-chi-bot]

This is an automated cherry-pick of #5881

What problem does this PR solve?

Issue Number: close #4811

What is changed and how it works?

The Result() function now returns a new copy of the process result instead of directly returning the pointer without the lock, which may cause data race when multiple functions are executing concurrently, some calling Result() and writing into some variables that other functions are trying to read.

To solve the problem, first call Marshal() on the original process result, which will generate an intermediate process result. Then call Unmarshal() on the intermediate one and generate a new process result. Now the new process result is a copy of the original one, thus it can be the return parameter of Result().

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No. The type of the return parameter is not changed, which is still *pb.ProcessResult, so this update will not affect those functions that call Result().

Do you need to update user documentation, design documentation or monitoring documentation?

No.

Release note

Fix the issue of the possible data race that might occur when multiple functions are executing concurrently, some calling Result() and writing into some variables that other functions are trying to read. #4811 

[ti-chi-bot]

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[lance6716]

/merge

[ti-chi-bot]

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

Commit hash: d852907

[lance6716]

/run-dm-integration-test
/run-integration-test
/run-kafka-integration-test
/run-dm-compatibility-test

[lance6716]

/run-dm-integration-test

[lance6716]

/run-dm-integration-test