Bug fix: disposing meter with same name does not dispose the shared metric

[sseelam2]

Fixes #6412

Changes

Added reference counting to Metric. AddInstrumentReference() is called when an instrument is attached; RemoveInstrumentReference() is called on completion and only triggers DeactivateMetric(Metric) when the count reaches zero. Both BuildForSingleMetric(Metric) and BuildForMetricList(List<Metric>) in MetricState are updated accordingly.

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)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.62%. Comparing base (9b45df9) to head (9d00a05).
⚠️ Report is 81 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7172      +/-   ##
==========================================
+ Coverage   89.08%   89.62%   +0.54%     
==========================================
  Files         271      272       +1     
  Lines       13073    14130    +1057     
==========================================
+ Hits        11646    12664    +1018     
- Misses       1427     1466      +39     

Flag	Coverage Δ
unittests-Project-Experimental	89.30% <100.00%> (+0.26%)	⬆️
unittests-Project-Stable	89.45% <100.00%> (+0.46%)	⬆️

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

Files with missing lines	Coverage Δ
src/OpenTelemetry/Metrics/Metric.cs	100.00% <100.00%> (ø)
src/OpenTelemetry/Metrics/MetricState.cs	92.10% <100.00%> (+0.67%)	⬆️

... and 34 files with indirect coverage changes

[cijothomas]

Thanks for the PR! I want to understand whether this is actually a bug or expected behavior.

The OTel SDK identifies meters by (name, version, schema_url, attributes) — not by object instance. So when two new Meter("MyApp") calls produce the same identity, from the SDK's perspective there's only one Meter/Scope. When either instance is disposed, isn't it reasonable that the SDK treats it as "the Meter named MyApp is being torn down" and deactivates the associated Metric?

Should we consider the current behavior a bug?

[sseelam2]

My understanding is that OpenTelemetry defines Meter identity using (name, version, schema_url, attributes) mainly for attribution. Does that also imply that all Meter instances with the same identity are expected to share the same lifetime?

I’m still getting familiar with the SDK, but in .NET Meter is IDisposable, and disposing one instance should ideally only affect the instruments created from that instance and not tear down the Metric if there are other Meter instances with the same identity still alive.

If disposing one Meter instance is meant to deactivate metrics for all meters with the same identity, that behavior should probably be explicit. Otherwise, we could consider preventing multiple meters from being created with the same identity.

[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.