Fix thread-safety issue in LogRecordSharedPool.Rent()

[kimjaejung96]

Fixes #6233

Changes

This PR fixes a thread-safety issue in LogRecordSharedPool.Rent() where the same LogRecord instance could be rented to multiple threads concurrently under high contention.

• Fixed Race Condition: In Rent(), when TryRentCoreRare fails (due to a race), changed the behavior to break the loop and create a new LogRecord instance. Previously, it would continue and retry with a new index, which could lead to a duplicate rental.
• Optimized Calculation: Extracted slotIndex calculation to avoid redundant modulo operations.
• Added Regression Test: Added RentShouldNeverReturnSameInstanceConcurrently in LogRecordSharedPoolTests.cs to verify the fix.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: rajkumar-rangaraj / name: Rajkumar Rangaraj (d5323a2)

[kimjaejung96]

Hi.

@alanwest @open-telemetry/dotnet-approvers could you please review this? It addresses the thread-safety issue in LogRecordSharedPool (Fixes #6233).

@TimothyMothra, tagging you as well since this is in the Logs/LogRecord pool area.

Also, this is my first time requesting a review in this repo—if I’m not tagging the right people or there’s a preferred process, please let me know and I’ll follow it.

[github-actions]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

[martincostello]

Please update the CHANGELOG with the bug fix details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.28%. Comparing base (86c7a90) to head (d5323a2).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6833      +/-   ##
==========================================
+ Coverage   86.35%   87.28%   +0.92%     
==========================================
  Files         263      263              
  Lines       12387    12388       +1     
==========================================
+ Hits        10697    10813     +116     
+ Misses       1690     1575     -115     

Flag	Coverage Δ
unittests-Project-Experimental	85.91% <100.00%> (-0.35%)	⬇️
unittests-Project-Stable	86.19% <100.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/Logs/Pool/LogRecordSharedPool.cs	100.00% <100.00%> (ø)

... and 8 files with indirect coverage changes

[github-actions]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.

[kimjaejung96]

Hi @martincostello — re-requesting review 🙇
Please let me know if there's anything else I should update.