code: def _import_plugins(self):
          
          if self.detected:
              return
  
          # In some cases, plugin scanning may start during a request.
          # Make sure there is only one thread scanning for plugins.
          self.scanLock.acquire()
          if self.detected:
              return  # previous threaded released + completed
  
          try:
              import_apps_submodule("content_plugins")
              self.detected = True
          finally:
              self.scanLock.release()
docs: Internal function, ensure all plugin packages are imported.