Can't pickle repeated scalar fields, convert to list firs

Question

I am trying to parallelize a protobuf application one instance in each thread, but I am getting this error

/usr/local/lib/python3.10/dist-packages/google/protobuf/internal/containers.py", line 250, in __reduce__
  raise pickle.PickleError("Can't pickle repeated scalar fields, convert to list first")

I compiled protobuf

./configure CPPFLAGS="-DGOOGLE_PROTOBUF_NO_THREAD_SAFETY"

the error comes from reduce function.

 def __reduce__(self, **kwargs) -> NoReturn:
     # Convert repeated scalar fields to lists
     raise pickle.PickleError("Can't pickle repeated scalar fields, convert to list first") 


 def add(self, **kwargs: Any) -> _T:
     """Adds a new element at the end of the list and returns it. Keyword
        arguments may be used to initialize the element.
     """
     new_element = self._message_descriptor._concrete_class(**kwargs)
     new_element._SetListener(self._message_listener)
     self._values.append(new_element)
     if not self._message_listener.dirty:
         self._message_listener.Modified()
     return new_element