statistics: make hotPeerCache concurrency safe

[Yisaer]

Signed-off-by: Song Gao disxiaofei@163.com

What problem does this PR solve?

In some cases, pd might update the same region and dimension at the same time which will cause the concurrent problem which may let pd panic.

ref #3461

What is changed and how it works?

This request made dimStat concurrency safe.

Check List

Tests

• Unit test

Release note

• No release note

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

[lhy1024]

It should be met only when handling some heartbeats from the same region at the same time.
Maybe we also need to learn why there is this case.

[lhy1024]

the rest LGTM

[codecov]

Codecov Report

Merging #3460 (f27397b) into master (722a665) will decrease coverage by 0.13%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           master    #3460      +/-   ##
==========================================
- Coverage   75.14%   75.00%   -0.14%     
==========================================
  Files         244      244              
  Lines       23557    23571      +14     
==========================================
- Hits        17702    17680      -22     
- Misses       4287     4311      +24     
- Partials     1568     1580      +12     

Flag	Coverage Δ
unittests	75.00% <95.83%> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/statistics/hot_peer_cache.go	93.42% <95.65%> (+0.36%)	⬆️
server/core/region_option.go	83.33% <100.00%> (+0.40%)	⬆️
pkg/metricutil/metricutil.go	82.75% <0.00%> (-10.35%)	⬇️
server/tso/global_allocator.go	70.14% <0.00%> (-6.72%)	⬇️
server/member/member.go	70.10% <0.00%> (-2.72%)	⬇️
server/server.go	71.98% <0.00%> (-1.86%)	⬇️
server/schedule/operator/step.go	67.44% <0.00%> (-1.67%)	⬇️
server/tso/allocator_manager.go	76.07% <0.00%> (-1.33%)	⬇️
server/config/persist_options.go	91.33% <0.00%> (-0.79%)	⬇️
client/client.go	67.01% <0.00%> (-0.18%)	⬇️
... and 2 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 722a665...f27397b. Read the comment docs.

[rleungx]

Will it have a performance problem?

[HunDunDM]

/hold