title: PySpark Streaming example does not seem to terminate
body: <p>I am trying to understand the Python API of Spark Streaming by a simple example. </p>
  
  <pre><code>from pyspark.streaming import StreamingContext
  dvc = [[-0.1, -0.1], [0.1, 0.1], [1.1, 1.1], [0.9, 0.9]]
  dvc = [sc.parallelize(i, 1) for i in dvc]
  ssc = StreamingContext(sc, 2.0)
  input_stream = ssc.queueStream(dvc)
  
  def get_output(rdd):
      print(rdd.collect())
  input_stream.foreachRDD(get_output)
  ssc.start()
  </code></pre>
  
  <p>This prints the the required output, but then prints a lot of empty lists at the end and does not terminate. Can someone tell me where I might be going wrong.</p>