scala - ConstantInputDStream.print() 什么都不做

Question

我正在尝试打印一个简单的 DStream，但没有成功。请参阅下面的代码。我在 Azure 中使用 Databricks 笔记本。

import org.apache.spark.streaming.{ StreamingContext, Seconds }
val ssc = new StreamingContext(sc, batchDuration = Seconds(5))

ssc.checkpoint(".")

val rdd = sc.parallelize(0 to 3)
import org.apache.spark.streaming.dstream.ConstantInputDStream
val stream = new ConstantInputDStream(ssc, rdd)

println("start")

stream.print()

ssc.start()

输出是：

start

warning: there was one feature warning; re-run with -feature for details
import org.apache.spark.streaming.{StreamingContext, Seconds}
ssc: org.apache.spark.streaming.StreamingContext = org.apache.spark.streaming.StreamingContext@4d01c7b1
rdd: org.apache.spark.rdd.RDD[Int] = MapPartitionsRDD[1] at map at command-3696830887613521:7
import org.apache.spark.streaming.dstream.ConstantInputDStream
stream: org.apache.spark.streaming.dstream.ConstantInputDStream[Int] = org.apache.spark.streaming.dstream.ConstantInputDStream@12b9db22

我期待以一种或另一种方式看到 0,1,2。

我也试过添加

ssc.awaitTermination()

但它永远不会结束。看截图：