code: def getRootDirectory(cls):
          
          if cls._is_running_on_worker:
              return cls._root_directory
          else:
              # This will have to change if we support multiple SparkContexts:
              return cls._sc._jvm.org.apache.spark.SparkFiles.getRootDirectory()
docs: Get the root directory that contains files added through
          C{SparkContext.addFile()}.