Description

Fix FastAPI instrumentation memory leak by tracking instrumented apps with a WeakSet instead of a strong-referenced set. This avoids retaining strong references to fastapi.FastAPI instances, allowing them to be garbage-collected even if uninstrument_app() isn’t called. Also aligns with the approach used in the Starlette instrumentation.

Scope minimized to FastAPI only:

• Use WeakSet for _instrumented_fastapi_apps and discard() on removal
• Add a GC-based test that verifies the app is collected without calling uninstrument_app()
• Remove the separate memory leak test file and integrate the test into test_fastapi_instrumentation.py
• Update CHANGELOG (Unreleased → Fixed)

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Added unit test:
  • test_fastapi_app_is_collected_after_instrument in test_fastapi_instrumentation.py, which:
    • creates an app
    • instruments it
    • drops the strong reference and forces gc.collect()
    • asserts the weakref is cleared (no leak)
• Existing FastAPI test suite continues to apply

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated