From 77f83efbf6c185e4ac01b54c9f06300d2b157070 Mon Sep 17 00:00:00 2001
From: Timur Vural <timurzvural@gmail.com>
Date: Fri, 30 Oct 2026 22:30:00 +0000
Subject: [PATCH 1/2] gh-160986: Sample popped frames only after leaf() is
 running

test_popping_python_frame_is_not_native attached as soon as the child
process could be read, then took a fixed 10,000 samples. On a slow
startup those samples all landed before leaf(), so the test observed
zero frames.
---
 Lib/test/test_external_inspection.py          | 29 +++++++++++++++----
 ...-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst |  3 ++
 2 files changed, 26 insertions(+), 6 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst

diff --git a/Lib/test/test_external_inspection.py b/Lib/test/test_external_inspection.py
index df0af14d9f75622..c930bb81f86146f 100644
--- a/Lib/test/test_external_inspection.py
+++ b/Lib/test/test_external_inspection.py
@@ -2033,14 +2033,31 @@ def leaf(depth):
         leaf(300)
 """
         with _managed_subprocess([sys.executable, "-c", script]) as process:
-            for _ in busy_retry(SHORT_TIMEOUT):
+            # RemoteUnwinder can attach during interpreter startup. Wait
+            # until leaf() is on the stack so the sample window observes it.
+            unwinder = None
+            for _ in busy_retry(
+                SHORT_TIMEOUT,
+                "child did not reach leaf() before sampling",
+            ):
+                if unwinder is None:
+                    try:
+                        unwinder = RemoteUnwinder(
+                            process.pid,
+                            native=True,
+                            gc=False,
+                            cache_frames=False,
+                        )
+                    except RuntimeError:
+                        continue
                 try:
-                    unwinder = RemoteUnwinder(
-                        process.pid, native=True, gc=False, cache_frames=False,
-                    )
-                except RuntimeError:
+                    threads = unwinder.get_stack_trace()[0].threads
+                except TRANSIENT_ERRORS:
                     continue
-                break
+                if threads and any(
+                    frame.funcname == "leaf" for frame in threads[0].frame_info
+                ):
+                    break
             samples = 0
             for _ in range(10_000):
                 try:
diff --git a/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst b/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst
new file mode 100644
index 000000000000000..5c4fcaf0fc46be3
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst
@@ -0,0 +1,3 @@
+Fix a race in ``test_external_inspection`` where
+``test_popping_python_frame_is_not_native`` could spend its whole sample
+window during interpreter startup, before the child reached ``leaf()``.

From c15c9ba4e96d43c910b7c8b9701ac79ffd24dd0a Mon Sep 17 00:00:00 2001
From: Timur Vural <timurzvural@gmail.com>
Date: Fri, 30 Oct 2026 17:27:28 -0700
Subject: [PATCH 2/2] Remove NEWS entry per review feedback.

---
 .../next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst  | 3 ---
 1 file changed, 3 deletions(-)
 delete mode 100644 Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst

diff --git a/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst b/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst
deleted file mode 100644
index 5c4fcaf0fc46be3..000000000000000
--- a/Misc/NEWS.d/next/Tests/2026-10-30-22-21-00.gh-issue-160986.k4Nw8p.rst
+++ /dev/null
@@ -1,3 +0,0 @@
-Fix a race in ``test_external_inspection`` where
-``test_popping_python_frame_is_not_native`` could spend its whole sample
-window during interpreter startup, before the child reached ``leaf()``.