From 2a1019ab336ca1a8fe7408b4e9db2b53abaca12f Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 1 Sep 2021 17:13:54 +0200
Subject: [PATCH] bpo-44895: libregrtest: refleak check clears types later

libregrtest now clears the type cache later to reduce the risk of
false alarm when checking for reference leaks. Previously, the type
cache was cleared too early and libregrtest raised a false alarm
about reference leaks under very specific conditions.

Move also support.gc_collect() outside clear/cleanup functions to
make the garbage collection more explicit.

Co-Authored-By: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
---
 Lib/test/libregrtest/refleak.py                    | 13 ++++++++-----
 Lib/test/libregrtest/runtest.py                    | 14 +++++++-------
 Lib/test/libregrtest/utils.py                      |  2 --
 .../Tests/2021-09-01-17-17-44.bpo-44895.kV7H77.rst |  5 +++++
 4 files changed, 20 insertions(+), 14 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Tests/2021-09-01-17-17-44.bpo-44895.kV7H77.rst

diff --git a/Lib/test/libregrtest/refleak.py b/Lib/test/libregrtest/refleak.py
index b94826a5daf92c..096b5381cd9339 100644
--- a/Lib/test/libregrtest/refleak.py
+++ b/Lib/test/libregrtest/refleak.py
@@ -85,13 +85,15 @@ def get_pooled_int(value):
               flush=True)
 
     dash_R_cleanup(fs, ps, pic, zdc, abcs)
+    support.gc_collect()
 
     for i in rep_range:
         test_func()
+
         dash_R_cleanup(fs, ps, pic, zdc, abcs)
+        support.gc_collect()
 
-        # dash_R_cleanup() ends with collecting cyclic trash:
-        # read memory statistics immediately after.
+        # Read memory statistics immediately after the garbage collection
         alloc_after = getallocatedblocks() - _getquickenedcount()
         rc_after = gettotalrefcount()
         fd_after = fd_count()
@@ -166,9 +168,6 @@ def dash_R_cleanup(fs, ps, pic, zdc, abcs):
         zipimport._zip_directory_cache.clear()
         zipimport._zip_directory_cache.update(zdc)
 
-    # clear type cache
-    sys._clear_type_cache()
-
     # Clear ABC registries, restoring previously saved ABC registries.
     abs_classes = [getattr(collections.abc, a) for a in collections.abc.__all__]
     abs_classes = filter(isabstract, abs_classes)
@@ -179,8 +178,12 @@ def dash_R_cleanup(fs, ps, pic, zdc, abcs):
                     obj.register(ref())
             obj._abc_caches_clear()
 
+    # Clear caches
     clear_caches()
 
+    # Clear type cache at the end: previous function calls can modify types
+    sys._clear_type_cache()
+
 
 def warm_caches():
     # char cache
diff --git a/Lib/test/libregrtest/runtest.py b/Lib/test/libregrtest/runtest.py
index 489ab986cb4e5e..fe4693bad9ca6d 100644
--- a/Lib/test/libregrtest/runtest.py
+++ b/Lib/test/libregrtest/runtest.py
@@ -297,9 +297,13 @@ def _runtest_inner2(ns: Namespace, test_name: str) -> bool:
                 test_runner()
                 refleak = False
     finally:
-        cleanup_test_droppings(test_name, ns.verbose)
+        # First kill any dangling references to open files etc.
+        # This can also issue some ResourceWarnings which would otherwise get
+        # triggered during the following test run, and possibly produce
+        # failures.
+        support.gc_collect()
 
-    support.gc_collect()
+        cleanup_test_droppings(test_name, ns.verbose)
 
     if gc.garbage:
         support.environment_altered = True
@@ -330,6 +334,7 @@ def _runtest_inner(
 
     try:
         clear_caches()
+        support.gc_collect()
 
         with save_env(ns, test_name):
             refleak = _runtest_inner2(ns, test_name)
@@ -373,11 +378,6 @@ def _runtest_inner(
 
 
 def cleanup_test_droppings(test_name: str, verbose: int) -> None:
-    # First kill any dangling references to open files etc.
-    # This can also issue some ResourceWarnings which would otherwise get
-    # triggered during the following test run, and possibly produce failures.
-    support.gc_collect()
-
     # Try to clean up junk commonly left behind.  While tests shouldn't leave
     # any files or directories behind, when a test fails that can be tedious
     # for it to arrange.  The consequences can be especially nasty on Windows,
diff --git a/Lib/test/libregrtest/utils.py b/Lib/test/libregrtest/utils.py
index 89d7e7e5354054..ad18b50f5db99d 100644
--- a/Lib/test/libregrtest/utils.py
+++ b/Lib/test/libregrtest/utils.py
@@ -217,5 +217,3 @@ def clear_caches():
     else:
         for f in typing._cleanups:
             f()
-
-    support.gc_collect()
diff --git a/Misc/NEWS.d/next/Tests/2021-09-01-17-17-44.bpo-44895.kV7H77.rst b/Misc/NEWS.d/next/Tests/2021-09-01-17-17-44.bpo-44895.kV7H77.rst
new file mode 100644
index 00000000000000..038466f8d6a4f3
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2021-09-01-17-17-44.bpo-44895.kV7H77.rst
@@ -0,0 +1,5 @@
+libregrtest now clears the type cache later to reduce the risk of false alarm
+when checking for reference leaks. Previously, the type cache was cleared too
+early and libregrtest raised a false alarm about reference leaks under very
+specific conditions.
+Patch by Irit Katriel and Victor Stinner.