[close #635] constraint the getMember timeout by inject a backoffer (#636)

[ti-srebot]

cherry-pick #636 to release-3.3
You can switch your code base to this Pull Request by using git-extras:

# In client-java repo:
git pr https://github.com/tikv/client-java/pull/637

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

git push git@github.com:ti-srebot/client-java.git pr/637:release-3.3-3128161b1f04

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Signed-off-by: iosmanthus myosmanthustree@gmail.com

What problem does this PR solve?

Issue Number: close #635

Problem Description:

The getMembers is not limited by a backoffer, which might cause the exception will not throw in time. For example, a user might set the timeout of a request to 400ms, but if the PD is disconnected, the getMembers might sleep more than 400ms since the backoffer it used is not passed from the upper code.

What is changed and how does it work?

Inject a backoffer for getMembers and check timeout before acquiring a channel from the pool.

Check List for Tests

This PR has been tested by at least one of the following methods:

• Unit test

Related changes

• Need to cherry-pick the release branch

[ti-srebot]

/run-all-tests

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-3.3@52491a1). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             release-3.3     #637   +/-   ##
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  Coverage               ?   34.92%           
  Complexity             ?     1432           
==============================================
  Files                  ?      278           
  Lines                  ?    17361           
  Branches               ?     1974           
==============================================
  Hits                   ?     6063           
  Misses                 ?    10686           
  Partials               ?      612           

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[iosmanthus]

LGTM

[ti-srebot]

@zhangyangyu, Thanks for your review. The bot only counts LGTMs from Reviewers and higher roles, but you're still welcome to leave your comments. You are not a reviewer or committer or co-leader or leader.