client/tso: double-check the contexts to prevent waiting for TSO requests in closed chan

[JmPotato]

What problem does this PR solve?

Issue Number: close #7849.

What is changed and how does it work?

This PR ensures that a `tsoRequest` could be done by double-checking the contexts to prevent waiting for TSO requests in the closed channel.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HuSharp
• nolouch

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[JmPotato]

/hold

[codecov]

Codecov Report

Merging #7962 (59c3a65) into master (c2eac4b) will increase coverage by 0.03%.
The diff coverage is 75.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7962      +/-   ##
==========================================
+ Coverage   73.54%   73.57%   +0.03%     
==========================================
  Files         436      436              
  Lines       48432    48451      +19     
==========================================
+ Hits        35618    35650      +32     
+ Misses       9754     9740      -14     
- Partials     3060     3061       +1     

Flag	Coverage Δ
unittests	73.57% <75.00%> (+0.03%)	⬆️

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

[CabinfeverB]

I'm not sure if this is effective in avoiding blocks, but the code itself is fine with me. I suggest we can test it before we consider merging?

[JmPotato]

I'm not sure if this is effective in avoiding blocks, but the code itself is fine with me. I suggest we can test it before we consider merging?

I'm not sure if this is effective in avoiding blocks, but the code itself is fine with me. I suggest we can test it before we consider merging?

I have manually tested it, and with this PR version of PD client, TiDB will no longer encounter the TSO hang issue.

[nolouch]

why need to try? from the goroutine profile we can make sure here is no blocking.

[JmPotato]

A request may be revoked right after it is sent to tsoBatchController, then if we double-check the contexts and return an error, done <- err will be blocked.

[HuSharp]

/merge

[ti-chi-bot]

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[ti-chi-bot]

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

Commit hash: 59c3a65

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #8090.