impl(bigtable): add ScheduleStubRefresh function using AsyncPingAndWarm

[scotthart]

Adds a new ScheduleStubRefresh function that is very similar to the existing ScheduleChannelRefresh function, except that is uses the AsyncPingAndWarm RPC on the Bigtable service to perform the refresh instead of using AsyncWaitConnectionReady. This new function will be used as part of the DynamicChannelPool feature for Bigtable.

[gemini-code-assist]

Summary of Changes

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This pull request enhances the Bigtable client library by providing an alternative mechanism for refreshing connections. The new ScheduleStubRefresh function leverages the Bigtable-specific PingAndWarm RPC, which is intended to be used with the DynamicChannelPool feature. This change allows for more targeted and potentially more effective connection health checks within the Bigtable service context.

Highlights

• New Connection Refresh Function: Introduced ScheduleStubRefresh, a new function designed to refresh Bigtable connections using the AsyncPingAndWarm RPC. This is distinct from the existing ScheduleChannelRefresh which uses AsyncWaitConnectionReady.
• Error Logging Refactoring: A new helper function, LogFailedConnectionRefresh, was added to centralize the logging of connection refresh failures, and ScheduleChannelRefresh was updated to utilize it.
• Testing for Stub Refresh: Added new unit tests for ScheduleStubRefresh to ensure its correct behavior, including scenarios for successful refresh and timer cancellation.

Changelog

• google/cloud/bigtable/internal/connection_refresh_state.cc
  • Added LogFailedConnectionRefresh helper function.
  • Refactored ScheduleChannelRefresh to use the new LogFailedConnectionRefresh function.
  • Implemented ScheduleStubRefresh function using AsyncPingAndWarm for connection refreshing.
• google/cloud/bigtable/internal/connection_refresh_state.h
  • Included bigtable_stub.h for BigtableStub dependency.
  • Updated documentation for ScheduleChannelRefresh to clarify its mechanism.
  • Declared the new ScheduleStubRefresh function.
• google/cloud/bigtable/internal/connection_refresh_state_test.cc
  • Added includes for mock_bigtable_stub.h and <thread>.
  • Introduced using declarations for MockBigtableStub, IsOk, Eq, and MockFunction.
  • Created ScheduleStubRefreshTest class with test cases for RefreshedUsingAsyncPingAndWarm and RefreshTimerCancelled.

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[gemini-code-assist]

Code Review

This pull request introduces a new function, ScheduleStubRefresh, which periodically refreshes a connection using the AsyncPingAndWarm RPC. This is analogous to the existing ScheduleChannelRefresh function. The changes also include a small refactoring to extract a common logging function, which improves code clarity. The overall implementation is solid and includes good test coverage for the new functionality. I have one suggestion to improve the implementation's correctness regarding move semantics within lambda expressions.

[codecov]

Codecov Report

❌ Patch coverage is 98.78049% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.64%. Comparing base (44efb79) to head (ee75589).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...loud/bigtable/internal/connection_refresh_state.cc	97.67%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #16029   +/-   ##
=======================================
  Coverage   92.63%   92.64%           
=======================================
  Files        2335     2335           
  Lines      214713   214792   +79     
=======================================
+ Hits       198903   198985   +82     
+ Misses      15810    15807    -3     

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