From a401818402740042d643e1c26c5c407fe663b60d Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 01:11:59 -0500
Subject: [PATCH 01/17] Make call_count of Mock thread safe

---
 .../testmock/testthreadingmock.py             | 22 +++++++++++++++++++
 Lib/unittest/mock.py                          | 12 +++++-----
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index a02b532ed447cd..2ee90ac1d02952 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -1,5 +1,6 @@
 import time
 import unittest
+import threading
 import concurrent.futures
 
 from test.support import threading_helper
@@ -196,6 +197,27 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
+    def test_call_count_thread_safe(self):
+        
+        m = ThreadingMock()
+        
+        # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
+        LOOPS = 3_000
+        THREADS = 10
+        
+        def test_function():
+            for _ in range(LOOPS):
+                m()
+        
+        threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
+        for thread in threads:
+            thread.start()
+        for thread in threads:
+            thread.join()
+        
+        self.assertEqual(m.call_count, LOOPS * THREADS,
+                        f"Expected {LOOPS * THREADS}, got {m.call_count}")
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 0bb6750655380d..a7fad7fec46da0 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -256,7 +256,6 @@ def reset_mock():
             ret.reset_mock()
 
     funcopy.called = False
-    funcopy.call_count = 0
     funcopy.call_args = None
     funcopy.call_args_list = _CallList()
     funcopy.method_calls = _CallList()
@@ -490,7 +489,6 @@ def __init__(
 
         __dict__['_mock_called'] = False
         __dict__['_mock_call_args'] = None
-        __dict__['_mock_call_count'] = 0
         __dict__['_mock_call_args_list'] = _CallList()
         __dict__['_mock_mock_calls'] = _CallList()
 
@@ -606,11 +604,17 @@ def __class__(self):
         return self._spec_class
 
     called = _delegating_property('called')
-    call_count = _delegating_property('call_count')
     call_args = _delegating_property('call_args')
     call_args_list = _delegating_property('call_args_list')
     mock_calls = _delegating_property('mock_calls')
 
+    @property
+    def call_count(self):
+        sig = self._mock_delegate
+        if sig is None:
+            return len(self._mock_call_args_list)
+        return len(sig.call_args_list)
+
 
     def __get_side_effect(self):
         delegated = self._mock_delegate
@@ -646,7 +650,6 @@ def reset_mock(self, visited=None, *,
 
         self.called = False
         self.call_args = None
-        self.call_count = 0
         self.mock_calls = _CallList()
         self.call_args_list = _CallList()
         self.method_calls = _CallList()
@@ -1180,7 +1183,6 @@ def _mock_call(self, /, *args, **kwargs):
 
     def _increment_mock_call(self, /, *args, **kwargs):
         self.called = True
-        self.call_count += 1
 
         # handle call_args
         # needs to be set here so assertions on call arguments pass before

From d532d23633eeea55eb5ead7db88c51a1d1ab9fc3 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Sat, 13 Dec 2025 06:17:46 +0000
Subject: [PATCH 02/17] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20b?=
 =?UTF-8?q?lurb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst  | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst

diff --git a/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst b/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
new file mode 100644
index 00000000000000..1cca83474d2820
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
@@ -0,0 +1 @@
+Fixed a thread safety issue in :mod:`unittest.mock` where :attr:`~unittest.mock.Mock.call_count` could return inaccurate values when a mock was called concurrently from multiple threads. The attribute now derives its value from the length of :attr:`~unittest.mock.Mock.call_args_list` to ensure consistency.

From fe7be86596dcb3cbb3483ceb3175d3e791f3cff7 Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 01:25:15 -0500
Subject: [PATCH 03/17] update doc

---
 Doc/library/unittest.mock.rst | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 91f90a0726aa93..86b13f33c42e7b 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -532,7 +532,8 @@ the *new_callable* argument to :func:`patch`.
 
     .. attribute:: call_count
 
-        An integer telling you how many times the mock object has been called:
+        An integer telling you how many times the mock object has been called,
+        it is the length of call_args_list:
 
             >>> mock = Mock(return_value=None)
             >>> mock.call_count
@@ -541,6 +542,8 @@ the *new_callable* argument to :func:`patch`.
             >>> mock()
             >>> mock.call_count
             2
+            >>> mock.call_count == len(mock.call_args_list)
+            True
 
     .. attribute:: return_value
 

From 29578a94af07fc61fa68ae9e6ba9fa0f37aa531c Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 02:46:32 -0500
Subject: [PATCH 04/17] calculate call_count after append call_args_list

---
 .../test_unittest/testmock/testthreadingmock.py     | 10 +++++-----
 Lib/unittest/mock.py                                | 13 +++++--------
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 2ee90ac1d02952..9672641a47eed4 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -198,23 +198,23 @@ def test_reset_mock_resets_wait(self):
         m.assert_called_once()
 
     def test_call_count_thread_safe(self):
-        
+
         m = ThreadingMock()
-        
+
         # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
         LOOPS = 3_000
         THREADS = 10
-        
+
         def test_function():
             for _ in range(LOOPS):
                 m()
-        
+
         threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
         for thread in threads:
             thread.start()
         for thread in threads:
             thread.join()
-        
+
         self.assertEqual(m.call_count, LOOPS * THREADS,
                         f"Expected {LOOPS * THREADS}, got {m.call_count}")
 
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index a7fad7fec46da0..47df724474fd93 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -256,6 +256,7 @@ def reset_mock():
             ret.reset_mock()
 
     funcopy.called = False
+    funcopy.call_count = 0
     funcopy.call_args = None
     funcopy.call_args_list = _CallList()
     funcopy.method_calls = _CallList()
@@ -489,6 +490,7 @@ def __init__(
 
         __dict__['_mock_called'] = False
         __dict__['_mock_call_args'] = None
+        __dict__['_mock_call_count'] = 0
         __dict__['_mock_call_args_list'] = _CallList()
         __dict__['_mock_mock_calls'] = _CallList()
 
@@ -605,17 +607,10 @@ def __class__(self):
 
     called = _delegating_property('called')
     call_args = _delegating_property('call_args')
+    call_count = _delegating_property('call_count')
     call_args_list = _delegating_property('call_args_list')
     mock_calls = _delegating_property('mock_calls')
 
-    @property
-    def call_count(self):
-        sig = self._mock_delegate
-        if sig is None:
-            return len(self._mock_call_args_list)
-        return len(sig.call_args_list)
-
-
     def __get_side_effect(self):
         delegated = self._mock_delegate
         if delegated is None:
@@ -650,6 +645,7 @@ def reset_mock(self, visited=None, *,
 
         self.called = False
         self.call_args = None
+        self.call_count = 0
         self.mock_calls = _CallList()
         self.call_args_list = _CallList()
         self.method_calls = _CallList()
@@ -1190,6 +1186,7 @@ def _increment_mock_call(self, /, *args, **kwargs):
         _call = _Call((args, kwargs), two=True)
         self.call_args = _call
         self.call_args_list.append(_call)
+        self.call_count = len(self.call_args_list)
 
         # initial stuff for method_calls:
         do_method_calls = self._mock_parent is not None

From c2e4ca7d882efc7a49314fafd68d5029cbc6e487 Mon Sep 17 00:00:00 2001
From: chaope <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 08:34:45 -0500
Subject: [PATCH 05/17] revert change on documentation for call_count.

---
 Doc/library/unittest.mock.rst | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 86b13f33c42e7b..91f90a0726aa93 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -532,8 +532,7 @@ the *new_callable* argument to :func:`patch`.
 
     .. attribute:: call_count
 
-        An integer telling you how many times the mock object has been called,
-        it is the length of call_args_list:
+        An integer telling you how many times the mock object has been called:
 
             >>> mock = Mock(return_value=None)
             >>> mock.call_count
@@ -542,8 +541,6 @@ the *new_callable* argument to :func:`patch`.
             >>> mock()
             >>> mock.call_count
             2
-            >>> mock.call_count == len(mock.call_args_list)
-            True
 
     .. attribute:: return_value
 

From e9e6dfa99d568641ea3d0ce52163421edfdb572e Mon Sep 17 00:00:00 2001
From: chaope <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 08:38:43 -0500
Subject: [PATCH 06/17] revert unnecessary change.

---
 Lib/unittest/mock.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 47df724474fd93..a70d2219e51116 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -606,8 +606,8 @@ def __class__(self):
         return self._spec_class
 
     called = _delegating_property('called')
-    call_args = _delegating_property('call_args')
     call_count = _delegating_property('call_count')
+    call_args = _delegating_property('call_args')
     call_args_list = _delegating_property('call_args_list')
     mock_calls = _delegating_property('mock_calls')
 

From 3a4b590768d37b3fe6a75b4e581c37e6512f7208 Mon Sep 17 00:00:00 2001
From: chaope <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 08:39:39 -0500
Subject: [PATCH 07/17] revert blank line deletion

---
 Lib/unittest/mock.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index a70d2219e51116..34fd49bf56fbb6 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -611,6 +611,7 @@ def __class__(self):
     call_args_list = _delegating_property('call_args_list')
     mock_calls = _delegating_property('mock_calls')
 
+
     def __get_side_effect(self):
         delegated = self._mock_delegate
         if delegated is None:

From 70e91077ac791fe1ef7785e38e0fb9c6699dcc28 Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 09:20:38 -0500
Subject: [PATCH 08/17] added TestThreadingMockRaceCondition

---
 .../testmock/testthreadingmock.py             | 34 ++++++++++++++++---
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 9672641a47eed4..d2fc8c3636ebc3 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -1,3 +1,4 @@
+import sys
 import time
 import unittest
 import threading
@@ -197,12 +198,34 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
-    def test_call_count_thread_safe(self):
 
+class TestThreadingMockRaceCondition(unittest.TestCase):
+    """Test that exposes race conditions in ThreadingMock."""
+
+    def setUp(self):
+        self._executor = concurrent.futures.ThreadPoolExecutor(max_workers=5)
+
+        # Store and restore original switch interval using addCleanup
+        self.addCleanup(sys.setswitchinterval, sys.getswitchinterval())
+
+        # Set switch interval to minimum to force frequent context switches
+        sys.setswitchinterval(sys.float_info.min)
+
+    def tearDown(self):
+        self._executor.shutdown()
+
+    def test_call_count_race_condition_with_fast_switching(self):
+        """Force race condition by maximizing thread context switches.
+
+        This test reduces the thread switch interval to its minimum value,
+        which maximizes the likelihood of context switches during the critical
+        section of _increment_mock_call.
+        """
         m = ThreadingMock()
 
-        # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
-        LOOPS = 3_000
+        # Use fewer loops but with maximum context switching pressure
+        # Expected runtime is 0.2 second
+        LOOPS = 100
         THREADS = 10
 
         def test_function():
@@ -215,8 +238,11 @@ def test_function():
         for thread in threads:
             thread.join()
 
+        # Without proper locking, this assertion will fail due to race condition
         self.assertEqual(m.call_count, LOOPS * THREADS,
-                        f"Expected {LOOPS * THREADS}, got {m.call_count}")
+                        f"Race condition detected: expected {LOOPS * THREADS}, "
+                        f"got {m.call_count}. call_args_list has "
+                        f"{len(m.call_args_list)} items.")
 
 
 if __name__ == "__main__":

From dc0d804c67e3e9095140be66ecdecedeaa1025b4 Mon Sep 17 00:00:00 2001
From: chaope <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 09:50:05 -0500
Subject: [PATCH 09/17] Update
 Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 .../Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst    | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst b/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
index 1cca83474d2820..236900bac5d6f6 100644
--- a/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
+++ b/Misc/NEWS.d/next/Library/2025-12-13-06-17-44.gh-issue-142651.ZRtBu4.rst
@@ -1 +1,3 @@
-Fixed a thread safety issue in :mod:`unittest.mock` where :attr:`~unittest.mock.Mock.call_count` could return inaccurate values when a mock was called concurrently from multiple threads. The attribute now derives its value from the length of :attr:`~unittest.mock.Mock.call_args_list` to ensure consistency.
+:mod:`unittest.mock`: fix a thread safety issue where :attr:`Mock.call_count
+<unittest.mock.Mock.call_count>` may return inaccurate values when the mock
+is called concurrently from multiple threads.

From f05407ebd7594962f34f13c433481de882d39ce3 Mon Sep 17 00:00:00 2001
From: chaope <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 09:50:13 -0500
Subject: [PATCH 10/17] Update
 Lib/test/test_unittest/testmock/testthreadingmock.py
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Lib/test/test_unittest/testmock/testthreadingmock.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 9672641a47eed4..c0663a4614a53c 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -215,8 +215,7 @@ def test_function():
         for thread in threads:
             thread.join()
 
-        self.assertEqual(m.call_count, LOOPS * THREADS,
-                        f"Expected {LOOPS * THREADS}, got {m.call_count}")
+        self.assertEqual(m.call_count, LOOPS * THREADS)
 
 
 if __name__ == "__main__":

From 3a81b0d9618d9cf894b15f32bfe6685623b7d842 Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 09:52:06 -0500
Subject: [PATCH 11/17] update test

---
 Lib/test/test_unittest/testmock/testthreadingmock.py | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index d2fc8c3636ebc3..9abcc40b1edeb6 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -238,11 +238,7 @@ def test_function():
         for thread in threads:
             thread.join()
 
-        # Without proper locking, this assertion will fail due to race condition
-        self.assertEqual(m.call_count, LOOPS * THREADS,
-                        f"Race condition detected: expected {LOOPS * THREADS}, "
-                        f"got {m.call_count}. call_args_list has "
-                        f"{len(m.call_args_list)} items.")
+        self.assertEqual(m.call_count, LOOPS * THREADS)
 
 
 if __name__ == "__main__":

From a76318e79772302eb779eb65e815b69d41e8c2ce Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 10:05:16 -0500
Subject: [PATCH 12/17] move self._executor.shutdown to addCleanup

---
 Lib/test/test_unittest/testmock/testthreadingmock.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 9abcc40b1edeb6..7f5bb5fb42ef31 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -204,6 +204,7 @@ class TestThreadingMockRaceCondition(unittest.TestCase):
 
     def setUp(self):
         self._executor = concurrent.futures.ThreadPoolExecutor(max_workers=5)
+        self.addCleanup(self._executor.shutdown)
 
         # Store and restore original switch interval using addCleanup
         self.addCleanup(sys.setswitchinterval, sys.getswitchinterval())
@@ -211,9 +212,6 @@ def setUp(self):
         # Set switch interval to minimum to force frequent context switches
         sys.setswitchinterval(sys.float_info.min)
 
-    def tearDown(self):
-        self._executor.shutdown()
-
     def test_call_count_race_condition_with_fast_switching(self):
         """Force race condition by maximizing thread context switches.
 

From 8e2348c4a2d8b8c98769476a63fa83a599170c6a Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 12:27:07 -0500
Subject: [PATCH 13/17] use 3k loops

---
 .../testmock/testthreadingmock.py             | 31 ++-----------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 7f5bb5fb42ef31..1222b80cb45b39 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -1,4 +1,3 @@
-import sys
 import time
 import unittest
 import threading
@@ -198,38 +197,14 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
-
-class TestThreadingMockRaceCondition(unittest.TestCase):
-    """Test that exposes race conditions in ThreadingMock."""
-
-    def setUp(self):
-        self._executor = concurrent.futures.ThreadPoolExecutor(max_workers=5)
-        self.addCleanup(self._executor.shutdown)
-
-        # Store and restore original switch interval using addCleanup
-        self.addCleanup(sys.setswitchinterval, sys.getswitchinterval())
-
-        # Set switch interval to minimum to force frequent context switches
-        sys.setswitchinterval(sys.float_info.min)
-
-    def test_call_count_race_condition_with_fast_switching(self):
-        """Force race condition by maximizing thread context switches.
-
-        This test reduces the thread switch interval to its minimum value,
-        which maximizes the likelihood of context switches during the critical
-        section of _increment_mock_call.
-        """
+    def test_call_count_thread_safe(self):
         m = ThreadingMock()
-
-        # Use fewer loops but with maximum context switching pressure
-        # Expected runtime is 0.2 second
-        LOOPS = 100
+        # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
+        LOOPS = 3_000
         THREADS = 10
-
         def test_function():
             for _ in range(LOOPS):
                 m()
-
         threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
         for thread in threads:
             thread.start()

From e7dcc5752b36b78eac687acdb0f07d2e15fe599f Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 12:50:40 -0500
Subject: [PATCH 14/17] add @requires_resource('cpu')

---
 Lib/test/test_unittest/testmock/testthreadingmock.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 1222b80cb45b39..0a243ba83700ca 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -3,7 +3,7 @@
 import threading
 import concurrent.futures
 
-from test.support import threading_helper
+from test.support import requires_resource, threading_helper
 from unittest.mock import patch, ThreadingMock
 
 
@@ -197,6 +197,7 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
+    @requires_resource('cpu')
     def test_call_count_thread_safe(self):
         m = ThreadingMock()
         # 3k loops reliably reproduces the issue while keeping runtime ~0.6s

From 851f698a6b6bd80ecaf1947e6293047807e13c1d Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 15:05:10 -0500
Subject: [PATCH 15/17] update test according to comments

---
 .../testmock/testthreadingmock.py             | 33 +++++++++++--------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 0a243ba83700ca..6bfdd45b8acce9 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -1,9 +1,10 @@
+import sys
 import time
 import unittest
 import threading
 import concurrent.futures
 
-from test.support import requires_resource, threading_helper
+from test.support import setswitchinterval, threading_helper
 from unittest.mock import patch, ThreadingMock
 
 
@@ -197,20 +198,24 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
-    @requires_resource('cpu')
     def test_call_count_thread_safe(self):
-        m = ThreadingMock()
-        # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
-        LOOPS = 3_000
-        THREADS = 10
-        def test_function():
-            for _ in range(LOOPS):
-                m()
-        threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
-        for thread in threads:
-            thread.start()
-        for thread in threads:
-            thread.join()
+        oldswitchinterval = sys.getswitchinterval()
+        setswitchinterval(1e-6)
+        try:
+            m = ThreadingMock()
+            # 100 loops with 10 threads reliably reproduces the issue while keeping runtime ~0.2s
+            LOOPS = 100
+            THREADS = 10
+            def test_function():
+                for _ in range(LOOPS):
+                    m()
+            threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
+            for thread in threads:
+                thread.start()
+            for thread in threads:
+                thread.join()
+        finally:
+            sys.setswitchinterval(oldswitchinterval)
 
         self.assertEqual(m.call_count, LOOPS * THREADS)
 

From 3b298676c60f57be008fcab45a3ae9e3ede3a189 Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sat, 13 Dec 2025 15:41:42 -0500
Subject: [PATCH 16/17] update according to comments

---
 .../test_unittest/testmock/testthreadingmock.py   | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index 6bfdd45b8acce9..e6b04ab1178432 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -199,16 +199,17 @@ def test_reset_mock_resets_wait(self):
         m.assert_called_once()
 
     def test_call_count_thread_safe(self):
+        # See https://github.com/python/cpython/issues/142651.
+        m = ThreadingMock()
+        LOOPS = 100
+        THREADS = 10
+        def test_function():
+            for _ in range(LOOPS):
+                m()
+
         oldswitchinterval = sys.getswitchinterval()
         setswitchinterval(1e-6)
         try:
-            m = ThreadingMock()
-            # 100 loops with 10 threads reliably reproduces the issue while keeping runtime ~0.2s
-            LOOPS = 100
-            THREADS = 10
-            def test_function():
-                for _ in range(LOOPS):
-                    m()
             threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
             for thread in threads:
                 thread.start()

From 16232b89c15a4a1869e174958851bb209aaa55b4 Mon Sep 17 00:00:00 2001
From: Chao Peng <pengchaoandy@gmail.com>
Date: Sun, 14 Dec 2025 07:23:32 -0500
Subject: [PATCH 17/17] use threading_helper.start_threads

---
 Lib/test/test_unittest/testmock/testthreadingmock.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Lib/test/test_unittest/testmock/testthreadingmock.py b/Lib/test/test_unittest/testmock/testthreadingmock.py
index e6b04ab1178432..3603995b090a6c 100644
--- a/Lib/test/test_unittest/testmock/testthreadingmock.py
+++ b/Lib/test/test_unittest/testmock/testthreadingmock.py
@@ -211,10 +211,8 @@ def test_function():
         setswitchinterval(1e-6)
         try:
             threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
-            for thread in threads:
-                thread.start()
-            for thread in threads:
-                thread.join()
+            with threading_helper.start_threads(threads):
+                pass
         finally:
             sys.setswitchinterval(oldswitchinterval)