impl(bigtable): save and restore Options across query plan refresh threads

[scotthart]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @scotthart, 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 refines the handling of thread-local Options within the Bigtable client library, particularly for asynchronous operations such as query plan refreshes. By explicitly saving and restoring the Options context at the point of execution for these operations, the changes ensure that the correct configuration and policies are applied, regardless of which thread ultimately processes the callback. This prevents potential inconsistencies and enhances the robustness of the client's asynchronous workflows.

Highlights

• Thread-Local Options Handling: The PrepareQuery and AsyncPrepareQuery refresh functions have been updated to explicitly save and restore Options within their respective lambda captures. This ensures that the correct operational context is maintained when these asynchronous operations are executed, potentially on different threads.
• Query Plan Refresh Context: The QueryPlan::ScheduleRefresh mechanism now captures the current Options and restores them using internal::OptionsSpan when its timer callback executes. This change addresses potential issues with thread-local Options in asynchronous timer events, guaranteeing consistent behavior.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a potential issue with Options propagation in asynchronous query plan refresh operations. By capturing the options when scheduling the refresh timer and restoring them within the timer's continuation using OptionsSpan, the changes ensure that the refresh logic executes with the correct context, regardless of which thread it runs on. The refactoring in DataConnectionImpl to rely on this mechanism simplifies the code by removing explicit Options passing. The implementation looks correct and robust.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.04%. Comparing base (361f9b8) to head (05cb0e1).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15747   +/-   ##
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  Coverage   93.03%   93.04%           
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  Files        2445     2445           
  Lines      226049   226052    +3     
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+ Hits       210313   210321    +8     
+ Misses      15736    15731    -5     

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[mpeddada1]

Mostly documenting this for future reference: does this ensure that the options are preserved/available for the refresh query plan operation(which is performed on a different thread)?

[scotthart]

This just ensures that when the refresh_fn is called it uses the Options from the current thread. The save/restore Options mechanism is part of the .then lambda on the refresh deadline timer in query_plan.cc