fix(profiler): decrement refcount given strong reference of frame object in python 3.11 (#4901)

## 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](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines)
when writing a release note.
- [ ] Add additional sections for `feat` and `fix` pull requests.
- [ ] [Library
documentation](https://github.com/DataDog/dd-trace-py/tree/1.x/docs)
and/or [Datadog's documentation
site](https://github.com/DataDog/documentation/) is updated. Link to doc
PR in description.

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## Motivation
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reviewers -->

## Design 
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trade-offs -->

## Testing strategy
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## Relevant issue(s)
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## Testing strategy
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## Reviewer Checklist
- [ ] Title is accurate.
- [ ] Description motivates each change.
- [ ] No unnecessary changes were introduced in this PR.
- [ ] Avoid breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
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](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines),
or else `changelog/no-changelog` label added.
- [ ] All relevant GitHub issues are correctly linked.
- [ ] Backports are identified and tagged with Mergifyio.

Co-authored-by: Brett Langdon <[email protected]>

Author: 2 people

ddtrace/profiling/collector/stack.pyx

@@ -257,6 +257,7 @@ cdef collect_threads(thread_id_ignore_list, thread_time, thread_span_links) with
                                 if exc_tb:
                                     current_exceptions[tstate.thread_id] = (<object>exc_type, <object>exc_tb)
                                 Py_XDECREF(exc_tb)
+                            Py_XDECREF(frame)
                         ELSE:
                             frame = tstate.frame
                             if frame:

releasenotes/notes/fix-profiler-3-11-memory-leak-stack-collector-9131642011ee5ce8.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    profiling: This fix resolves an issue in Python 3.11 where a PyFrameObject strong reference count was not properly
+    decremented in the stack collector.

tests/profiling/collector/test_stack.py

@@ -1,10 +1,12 @@
 # -*- encoding: utf-8 -*-
 import collections
+import gc
 import os
 import sys
 import threading
 import time
 import timeit
+from types import FrameType
 import typing
 import uuid
 
@@ -400,7 +402,7 @@ def test_exception_collection():
     assert e.sampling_period > 0
     assert e.thread_id == nogevent.thread_get_ident()
     assert e.thread_name == "MainThread"
-    assert e.frames == [(__file__, 394, "test_exception_collection", "")]
+    assert e.frames == [(__file__, 396, "test_exception_collection", "")]
     assert e.nframes == 1
     assert e.exc_type == ValueError
 
@@ -432,7 +434,7 @@ def test_exception_collection_trace(
     assert e.sampling_period > 0
     assert e.thread_id == nogevent.thread_get_ident()
     assert e.thread_name == "MainThread"
-    assert e.frames == [(__file__, 421, "test_exception_collection_trace", "")]
+    assert e.frames == [(__file__, 423, "test_exception_collection_trace", "")]
     assert e.nframes == 1
     assert e.exc_type == ValueError
     assert e.span_id == span.span_id
@@ -743,3 +745,23 @@ def _nothing():
     # assert (exact_time * 0.7) <= values.pop() <= (exact_time * 1.3)
 
     assert values.pop() > 0
+
+
+@pytest.mark.skipif(sys.version_info < (3, 11, 0), reason="PyFrameObjects are lazy-created objects in Python 3.11+")
+def test_collect_ensure_all_frames_gc():
+    # Regression test for memory leak with lazy PyFrameObjects in Python 3.11+
+    def _foo():
+        pass
+
+    r = recorder.Recorder()
+    s = stack.StackCollector(r)
+
+    with s:
+        for _ in range(100):
+            _foo()
+
+    gc.collect()  # Make sure we don't race with gc when we check frame objects
+    frametype_objs = [obj for obj in gc.get_objects() if isinstance(obj, FrameType)]
+    for obj in frametype_objs:
+        # Ensure that all frames relating to _foo() have been gc'd already
+        assert obj.f_code.co_name != "_foo"