fix(profiler): decrement refcount given strong reference of frame object in python 3.11

[Yun-Kim]

Description

#4125 added the use of a getter function PyThread_GetFrame() to provide compatibility for Python 3.11 in the profiler (specifically the stack collector). However, PyThread_GetFrame() returns a strong reference to a PyFrameObject and its reference count was not decremented in that change. This means that the frame object will not be garbage collected and likely the cause behind the memory leak mentioned in #4899.

Checklist

• Followed the library release note guidelines when writing a release note.
• Add additional sections for feat and fix pull requests.
• Library documentation and/or Datadog's documentation site is updated. Link to doc PR in description.

Relevant issue(s)

Fixes #4899

Testing strategy

Since this change ensures that all FrameType objects in the stack collector have their reference count properly decremented, a regression test was added to ensure that all FrameType objects from the stack collector are garbage collected. test_collect_ensure_all_frames_gc runs an arbitrary function _foo() multiple times, then makes sure that garbage collection has occurred. Finally, the test checks that all FrameType objects relating to that function _foo() have been collected by the garbage collector, or in other words are not present in the garbage collector.

Checking the garbage collector was the most direct way to test that this change indeed does avoid leaking any memory due to FrameType objects in the stack collector.

Reviewer Checklist

• Title is accurate.
• Description motivates each change.
• No unnecessary changes were introduced in this PR.
• Avoid breaking API changes unless absolutely necessary.
• Tests provided or description of manual testing performed is included in the code or PR.
• Release note has been added and follows the library release note guidelines, or else changelog/no-changelog label added.
• All relevant GitHub issues are correctly linked.
• Backports are identified and tagged with Mergifyio.

[P403n1x87]

@Yun-Kim can we perhaps add a test case where we assert that

import gc
from types import FrameType

assert all(not isinstance(_, FrameType) for _ in gc.get_objects())

?

[Yun-Kim]

can we perhaps add a test case where we assert that

import gc
from types import FrameType

assert all(not isinstance(_, FrameType) for _ in gc.get_objects())

?

@P403n1x87 I think we can do that in #4895 instead of this PR if the pypi build error (with Project being found when we should expect a PyFrameObject) is what you're referencing.

[P403n1x87]

@Yun-Kim I think it might be worth adding the test case here too. This is the PR that fixes the frame object leaks so it would be nice if we could add the test case that would catch any potential regressions.

[brettlangdon]

@Yun-Kim can you fill in the "testing strategy" details of the PR description? it would be good to have some human words describing how we decided to test it this way / are there other ways or ways that cannot be automated?

[P403n1x87]

👍 👍