On demand create message meta class for upb python

PiperOrigin-RevId: 565733360

python/descriptor.c

@@ -213,6 +213,25 @@ PyObject* PyUpb_Descriptor_Get(const upb_MessageDef* m) {
 
 PyObject* PyUpb_Descriptor_GetClass(const upb_MessageDef* m) {
  PyObject* ret = PyUpb_ObjCache_Get(upb_MessageDef_MiniTable(m));
+ if (ret) return ret;
+
+ // On demand create the clss if not exist. However, if users repeatedly
+ // create and destroy a class, it could trigger a loop. This is not an
+ // issue now, but if we see CPU waste for repeatedly create and destroy
+ // in the future, we could make PyUpb_Descriptor_Get() append the descriptor
+ // to an internal list in DescriptorPool, let the pool keep descriptors alive.
+ PyObject* py_descriptor = PyUpb_Descriptor_Get(m);
+ if (py_descriptor == NULL) return NULL;
+ const char* name = upb_MessageDef_Name(m);
+ PyObject* dict = PyDict_New();
+ if (dict == NULL) goto err;
+ int status = PyDict_SetItemString(dict, "DESCRIPTOR", py_descriptor);
+ if (status < 0) goto err;
+ ret = PyUpb_MessageMeta_DoCreateClass(py_descriptor, name, dict);
+
+err:
+ Py_XDECREF(py_descriptor);
+ Py_XDECREF(dict);
  return ret;
 }
 
@@ -477,7 +496,7 @@ static PyObject* PyUpb_Descriptor_GetFullName(PyObject* self, void* closure) {
 static PyObject* PyUpb_Descriptor_GetConcreteClass(PyObject* self,
  void* closure) {
  const upb_MessageDef* msgdef = PyUpb_Descriptor_GetDef(self);
- return PyUpb_Descriptor_GetClass(msgdef);
+ return PyUpb_ObjCache_Get(upb_MessageDef_MiniTable(msgdef));
 }
 
 static PyObject* PyUpb_Descriptor_GetFile(PyObject* self, void* closure) {

python/message.h

@@ -93,6 +93,10 @@ PyObject* PyUpb_Message_GetFieldValue(PyObject* _self,
 int PyUpb_Message_SetFieldValue(PyObject* _self, const upb_FieldDef* field,
  PyObject* value, PyObject* exc);
 
+// Creates message meta class.
+PyObject* PyUpb_MessageMeta_DoCreateClass(PyObject* py_descriptor,
+ const char* name, PyObject* dict);
+
 // Returns the version associated with this message. The version will be
 // incremented when the message changes.
 int PyUpb_Message_GetVersion(PyObject* _self);