Make sure python is alive before DECREFing

If something triggers internals to be created during finalization, it might end up being destroyed after finalization and we don't want to do the DECREF at that point, we need the leaky behavior.

Author: b-pass

include/pybind11/detail/internals.h

@@ -309,11 +309,17 @@ struct internals {
     internals &operator=(const internals &other) = delete;
     internals &operator=(internals &&other) = delete;
     ~internals() {
-        Py_XDECREF(static_property_type);
-        static_property_type = nullptr;
-
-        Py_XDECREF(default_metaclass);
-        default_metaclass = nullptr;
+        // Normally this destructor runs during interpreter finalization and it may DECREF things.
+        // In odd finalization scenarios it might end up running after the interpreter has
+        // completely shut down, In that case, we should not decref these objects because pymalloc
+        // is gone.
+        if (Py_IsInitialized()) {
+            Py_XDECREF(static_property_type);
+            static_property_type = nullptr;
+
+            Py_XDECREF(default_metaclass);
+            default_metaclass = nullptr;
+        }
     }
 };
 
@@ -333,8 +339,14 @@ struct local_internals {
     PyTypeObject *function_record_py_type = nullptr;
 
     ~local_internals() {
-        Py_XDECREF(function_record_py_type);
-        function_record_py_type = nullptr;
+        // Normally this destructor runs during interpreter finalization and it may DECREF things.
+        // In odd finalization scenarios it might end up running after the interpreter has
+        // completely shut down, In that case, we should not decref these objects because pymalloc
+        // is gone.
+        if (Py_IsInitialized()) {
+            Py_XDECREF(function_record_py_type);
+            function_record_py_type = nullptr;
+        }
     }
 };
 
@@ -717,8 +729,9 @@ class internals_pp_manager {
             pp->reset();
         }
         // Because the unique_ptr is still pointed to by the pp_manager in this and possibly other
-        // modules, we cannot free the unique_ptr itself until after the interpreter has shut down.
-        // If this interpreter was not created/owned by pybind11 then this unique_ptr is leaked.
+        // modules, we cannot delete the unique_ptr itself until after the interpreter has shut
+        // down. If this interpreter was not created/owned by pybind11 then the unique_ptr itself
+        // (but not its contents) is leaked.
     }
 
     std::unique_ptr<InternalsType> *get_or_create_pp_in_state_dict() {