fix: fix the race condition caused by setting client = nil during client closure

[huskar-t]

Description

fix: fix the race condition caused by setting client = nil during client closure

Issue(s)

• Fix: https://project.feishu.cn/taosdata_td/defect/detail/6606851833

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @huskar-t, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical race condition within the client closure mechanism by leveraging Go's sync.Once primitive. The change ensures that the essential steps for shutting down a connection, such as marking it as closed and invoking the underlying client's close method, are executed atomically and precisely once. This significantly enhances the robustness and thread-safety of the connection management, preventing potential issues from multiple concurrent attempts to close the same connection.

Highlights

• Race Condition Fix: Implemented sync.Once in the taosConn.Close() method to guarantee that the client closure logic executes only a single time, thereby preventing potential race conditions that could arise from concurrent calls to Close().
• Client State Reset Refinement: Removed the explicit setting of tc.client, tc.cfg, and tc.endpoint to nil within the Close() method, as these operations are not thread-safe and are not strictly necessary for ensuring proper client closure with the sync.Once mechanism.

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[gemini-code-assist]

Code Review

This pull request addresses a race condition in taosConn.Close() by introducing sync.Once to ensure the closing logic runs only once, and by removing the assignment tc.client = nil which could cause a nil pointer dereference in a concurrent read goroutine. The fix is correct and effectively resolves the race condition. I've added one suggestion to simplify the code within the sync.Once block by removing a now-redundant check.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.68%. Comparing base (dcec3eb) to head (145a6f6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #350      +/-   ##
==========================================
+ Coverage   82.86%   85.68%   +2.82%     
==========================================
  Files          80       80              
  Lines       10458     9077    -1381     
==========================================
- Hits         8666     7778     -888     
+ Misses       1283      790     -493     
  Partials      509      509              

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