gh-120524: Avoid a Race On _PyRuntime.types.managed_static.types[i].interp_count (gh-120529)

gh-120182 added new global state (interp_count), but didn't add thread-safety for it.  This change eliminates the possible race.

Author: ericsnowcurrently

Lib/test/test_interpreters/test_stress.py

@@ -22,7 +22,6 @@ def test_create_many_sequential(self):
             interp = interpreters.create()
             alive.append(interp)
 
-    @unittest.skip('(temporary) gh-120524: there is a race that needs fixing')
     @support.requires_resource('cpu')
     def test_create_many_threaded(self):
         alive = []

Objects/typeobject.c

@@ -246,7 +246,8 @@ managed_static_type_state_init(PyInterpreterState *interp, PyTypeObject *self,
 
     assert((initial == 1) ==
             (_PyRuntime.types.managed_static.types[full_index].interp_count == 0));
-    _PyRuntime.types.managed_static.types[full_index].interp_count += 1;
+    (void)_Py_atomic_add_int64(
+            &_PyRuntime.types.managed_static.types[full_index].interp_count, 1);
 
     if (initial) {
         assert(_PyRuntime.types.managed_static.types[full_index].type == NULL);
@@ -300,7 +301,8 @@ managed_static_type_state_clear(PyInterpreterState *interp, PyTypeObject *self,
     state->type = NULL;
     assert(state->tp_weaklist == NULL);  // It was already cleared out.
 
-    _PyRuntime.types.managed_static.types[full_index].interp_count -= 1;
+    (void)_Py_atomic_add_int64(
+            &_PyRuntime.types.managed_static.types[full_index].interp_count, -1);
     if (final) {
         assert(!_PyRuntime.types.managed_static.types[full_index].interp_count);
         _PyRuntime.types.managed_static.types[full_index].type = NULL;