promutil(engine): avoid embedding Mutex and prometheus.Registry in Registry

[sleepymole]

What problem does this PR solve?

Issue Number: ref #5673

Problem Summary:

Avoid embedding Mutex and prometheus.Registry in Registry.

Refer to uber go style:

• https://github.com/uber-go/guide/blob/master/style.md#avoid-embedding-types-in-public-structs
• https://github.com/uber-go/guide/blob/master/style.md#zero-value-mutexes-are-valid

What is changed and how it works?

Make Mutex and prometheus.Registry become private normal members.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

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

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lance6716
• maxshuang

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[lance6716]

/cc @maxshuang

[sleepymole]

/merge

[ti-chi-bot]

@gozssky: /merge is only allowed for the committers, you can assign this pull request to the committer in list by filling /assign @committer in the comment to help merge this pull request.

Details

In response to this:

/merge

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[amyangfei]

/merge

[ti-chi-bot]

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

Details

Commit hash: ed6e8a0

[ti-chi-bot]

@gozssky: Your PR was out of date, I have automatically updated it for you.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

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[amyangfei]

/run-verify