[fix][meta] deadlock of zkSessionWatcher when zkConnection loss

[tiny-rain]

Fixes #20105

Motivation

The deadlock is caused by the different acquiring lock order in zkwatcher callback and connection check thread in zkSessionWatcher. Meanwhile, the lock of ZkSessionWatch is intending to project the currentStatus field, no need to perform a lock operation when executing checkConnectionStatus method.

Modifications

1. don't perform a lock operation in ZKSessionWatcher.checkConnectionStatus method, which runs in single thread.
2. perform a lock operation in ZKSessionWatcher.checkStatus method.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
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• The threading model
• The binary protocol
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• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
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Matching PR in forked repository

PR in forked repository:

[mattisonchao]

@tiny-rain could you please help fix this PR to pass the CI?

[michaeljmarshall]

As discussed on the mailing list https://lists.apache.org/thread/w4jzk27qhtosgsz7l9bmhf1t7o9mxjhp, there is no plan to release 2.9.6, so I am going to remove the release/2.9.6 label