Shut down the SparkContext.

def stop(self):
        """
        Shut down the SparkContext.
        """
        if getattr(self, "_jsc", None):
            try:
                self._jsc.stop()
            except Py4JError:
                # Case: SPARK-18523
                warnings.warn(
                    'Unable to cleanly shutdown Spark JVM process.'
                    ' It is possible that the process has crashed,'
                    ' been killed or may also be in a zombie state.',
                    RuntimeWarning
                )
            finally:
                self._jsc = None
        if getattr(self, "_accumulatorServer", None):
            self._accumulatorServer.shutdown()
            self._accumulatorServer = None
        with SparkContext._lock:
            SparkContext._active_spark_context = None