[metrics] dictionary changed size during iteration

[sk-]

Describe your environment

OS: Debian Python version: 3.12.9 (main, Apr 8 2025, 01:41:13) [GCC 12.2.0] SDK version: 1.38.0 API version: 1.38.0

What happened?

We have gotten some errors on Sentry while exporting metrics because the dictionary changed size during iteration.

The error happens on file opentelemetry/sdk/metrics/_internal/metric_reader_storage.py in collect at line 149.

Steps to Reproduce

Unfortunately this happens about three times a day and we haven't found how to trigger it.

Expected Result

Metrics should be exported successfully.

Actual Result

Sometimes the metrics fails with the error: RuntimeError: dictionary changed size during iteration

Additional context

Stack trace

Would you like to implement a fix?

None

Tip

_{React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it. Learn more here.}

[aabmass]

Thanks for the report, I can see how this would happen. We should probably just copy the whole dict or its keys for a stable iteration. We don't want to lock the whole dictionary