[3.12] gh-109593: Fix reentrancy issue in multiprocessing resource_tracker (GH-109629) (#109898)

gh-109593: Fix reentrancy issue in multiprocessing resource_tracker (GH-109629)

---------

(cherry picked from commit 0eb98837b6)

Co-authored-by: Antoine Pitrou <antoine@python.org>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Lib/test/lock_tests.py

@@ -330,6 +330,42 @@ class RLockTests(BaseLockTests):
         lock.release()
         self.assertRaises(RuntimeError, lock._release_save)
 
+    def test_recursion_count(self):
+        lock = self.locktype()
+        self.assertEqual(0, lock._recursion_count())
+        lock.acquire()
+        self.assertEqual(1, lock._recursion_count())
+        lock.acquire()
+        lock.acquire()
+        self.assertEqual(3, lock._recursion_count())
+        lock.release()
+        self.assertEqual(2, lock._recursion_count())
+        lock.release()
+        lock.release()
+        self.assertEqual(0, lock._recursion_count())
+
+        phase = []
+
+        def f():
+            lock.acquire()
+            phase.append(None)
+            while len(phase) == 1:
+                _wait()
+            lock.release()
+            phase.append(None)
+
+        with threading_helper.wait_threads_exit():
+            start_new_thread(f, ())
+            while len(phase) == 0:
+                _wait()
+            self.assertEqual(len(phase), 1)
+            self.assertEqual(0, lock._recursion_count())
+            phase.append(None)
+            while len(phase) == 2:
+                _wait()
+            self.assertEqual(len(phase), 3)
+            self.assertEqual(0, lock._recursion_count())
+
     def test_different_thread(self):
         # Cannot release from a different thread
         lock = self.locktype()