!1216 Check protobuf's backend in user environment

From: @lvyufeng
Reviewed-by: 
Signed-off-by:

mindinsight/mindconverter/graph_based_converter/framework.py

@@ -35,6 +35,8 @@ from mindinsight.mindconverter.common.exceptions import GraphInitError, TreeCrea
     BadParamError
 from mindinsight.mindconverter.graph_based_converter.third_party_graph import GraphFactory
 
+from google.protobuf.internal import api_implementation
+
 check_common_dependency_integrity = partial(check_dependency_integrity,
                                             "onnx", "onnxruntime", "onnxoptimizer")
 
@@ -262,6 +264,11 @@ def main_graph_base_converter(file_config):
     Args:
         file_config (dict): The config of file which to convert.
     """
+    if api_implementation.Type() != 'cpp' \
+        or os.getenv('PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION') != 'cpp':
+        log_console.warning("Protobuf is currently implemented in \"Python\". \
+            The conversion process may take a long time. \
+            Please use the \"C++\" backend version")
     graph_path = file_config['model_file']
     frame_type = get_framework_type(graph_path)
     if not file_config.get("shape"):