bpo-32604: Fix memory leaks in the new _xxsubinterpreters module. (GH-5507)

(cherry picked from commit 4e9da0d163)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

Lib/test/test__xxsubinterpreters.py

@@ -362,13 +362,15 @@ class DestroyTests(TestBase):
     def test_from_current(self):
         main, = interpreters.list_all()
         id = interpreters.create()
-        script = dedent("""
+        script = dedent(f"""
             import _xxsubinterpreters as _interpreters
-            _interpreters.destroy({})
+            try:
-            """).format(id)
+                _interpreters.destroy({id})
+            except RuntimeError:
+                pass
+            """)
 
-        with self.assertRaises(RuntimeError):
+        interpreters.run_string(id, script)
-            interpreters.run_string(id, script)
         self.assertEqual(set(interpreters.list_all()), {main, id})
 
     def test_from_sibling(self):
@@ -761,12 +763,12 @@ class ChannelIDTests(TestBase):
         self.assertEqual(int(cid), 10)
 
     def test_bad_id(self):
-        ids = [-1, 2**64, "spam"]
+        for cid in [-1, 'spam']:
-        for cid in ids:
             with self.subTest(cid):
                 with self.assertRaises(ValueError):
                     interpreters._channel_id(cid)
-
+        with self.assertRaises(OverflowError):
+            interpreters._channel_id(2**64)
         with self.assertRaises(TypeError):
             interpreters._channel_id(object())
 

Python/pystate.c

@@ -1242,6 +1242,7 @@ _PyCrossInterpreterData_Lookup(PyObject *obj)
             break;
         }
     }
+    Py_DECREF(cls);
     PyThread_release_lock(_PyRuntime.xidregistry.mutex);
     return getdata;
 }