Fix vizplugin multiple warning (#298)

src/viztracer/vizplugin.py

@@ -63,6 +63,11 @@ def __init__(self, tracer: "VizTracer", plugins: Sequence[Union[VizPluginBase, s
             else:
                 raise TypeError("Invalid plugin!")
             self._plugins.append(plugin_instance)
+
+            support_version = plugin_instance.support_version()
+            if compare_version(support_version, __version__) > 0:
+                color_print("WARNING", "The plugin support version is higher than "
+                                       "viztracer version. Consider update your viztracer")
             self._send_message(plugin_instance, "event", {"when": "initialize"})
 
     def _get_plugin_from_string(self, plugin: str) -> VizPluginBase:
@@ -102,9 +107,6 @@ def _send_message(self, plugin: VizPluginBase, m_type: str, payload: Dict) -> No
         # in the future we may need to do version compatibility
         # here
         support_version = plugin.support_version()
-        if compare_version(support_version, __version__) > 0:
-            color_print("WARNING", "The plugin support version is higher than "
-                                   "viztracer version. Consider update your viztracer")
 
         ret = plugin.message(m_type, payload)
         if m_type == "command":

tests/test_vizplugin.py

@@ -78,7 +78,8 @@ def test_version(self):
         with redirect_stdout(s):
             with VizTracer(plugins=[pl], verbose=0):
                 _ = []
-        self.assertIn("support version is higher", s.getvalue())
+        output = s.getvalue()
+        self.assertEqual(output.count("support version is higher"), 1)
 
     def test_cmdline(self):
         self.template(["viztracer", "--plugin", "tests.modules.dummy_vizplugin", "--", "cmdline_test.py"])