From 678ecdea4559661ae533fd2ce9b92a5250ac7182 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Sat, 4 Nov 2023 01:18:42 +0100
Subject: [PATCH] gh-111644: Fix support threading_cleanup() (GH-111714)

Copy the list of dangling threads to make sure that the list of
"Dangling thread" is complete. Previously, the list was incomplete if
threads completed just before the list was displayed.

Changes:

* Rewrite the warning to make it easier to understand.
* Use support.sleeping_retry().
* threading_cleanup() no longer copies threading._dangling,
  but only counts the number of dangling thread.
* Remove support.gc_support() call.
(cherry picked from commit f62c7ccf9abf6e0493978da9cf9ca43adcd403f9)

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Lib/test/support/threading_helper.py | 53 +++++++++++++++-------------
 1 file changed, 28 insertions(+), 25 deletions(-)

diff --git a/Lib/test/support/threading_helper.py b/Lib/test/support/threading_helper.py
index b9973c8bf5c914..6815ab36ec7a9f 100644
--- a/Lib/test/support/threading_helper.py
+++ b/Lib/test/support/threading_helper.py
@@ -22,34 +22,37 @@
 
 
 def threading_setup():
-    return _thread._count(), threading._dangling.copy()
+    return _thread._count(), len(threading._dangling)
 
 
 def threading_cleanup(*original_values):
-    _MAX_COUNT = 100
-
-    for count in range(_MAX_COUNT):
-        values = _thread._count(), threading._dangling
-        if values == original_values:
-            break
-
-        if not count:
-            # Display a warning at the first iteration
-            support.environment_altered = True
-            dangling_threads = values[1]
-            support.print_warning(f"threading_cleanup() failed to cleanup "
-                                  f"{values[0] - original_values[0]} threads "
-                                  f"(count: {values[0]}, "
-                                  f"dangling: {len(dangling_threads)})")
-            for thread in dangling_threads:
-                support.print_warning(f"Dangling thread: {thread!r}")
-
-            # Don't hold references to threads
-            dangling_threads = None
-        values = None
-
-        time.sleep(0.01)
-        support.gc_collect()
+    orig_count, orig_ndangling = original_values
+
+    timeout = 1.0
+    for _ in support.sleeping_retry(timeout, error=False):
+        # Copy the thread list to get a consistent output. threading._dangling
+        # is a WeakSet, its value changes when it's read.
+        dangling_threads = list(threading._dangling)
+        count = _thread._count()
+
+        if count <= orig_count:
+            return
+
+    # Timeout!
+    support.environment_altered = True
+    support.print_warning(
+        f"threading_cleanup() failed to clean up threads "
+        f"in {timeout:.1f} seconds\n"
+        f"  before: thread count={orig_count}, dangling={orig_ndangling}\n"
+        f"  after: thread count={count}, dangling={len(dangling_threads)}")
+    for thread in dangling_threads:
+        support.print_warning(f"Dangling thread: {thread!r}")
+
+    # The warning happens when a test spawns threads and some of these threads
+    # are still running after the test completes. To fix this warning, join
+    # threads explicitly to wait until they complete.
+    #
+    # To make the warning more likely, reduce the timeout.
 
 
 def reap_threads(func):