How do I use infinite Scala streams as source in Spark Streaming?

Question

Suppose I essentially want Stream.from(0) as InputDStream . How would I go about this? The only way I can see is to use StreamingContext#queueStream , but I'd have to either enqueue elements from another thread or subclass Queue to create a queue that behaves like an infinite stream, both of which feel like a hack.

What's the correct way to do this?

Answer 1

I don't think that it's available in Spark by default but it's easy to implement it with ReceiverInputDStream.

import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.StreamingContext
import org.apache.spark.streaming.dstream.ReceiverInputDStream
import org.apache.spark.streaming.receiver.Receiver

class InfiniteStreamInputDStream[T](
       @transient ssc_ : StreamingContext,
       stream: Stream[T],
       storageLevel: StorageLevel
      ) extends ReceiverInputDStream[T](ssc_)  {

  override def getReceiver(): Receiver[T] = {
    new InfiniteStreamReceiver(stream, storageLevel)
  }
}

class InfiniteStreamReceiver[T](stream: Stream[T], storageLevel: StorageLevel) extends Receiver[T](storageLevel) {

  // Stateful iterator
  private val streamIterator = stream.iterator

  private class ReadAndStore extends Runnable {
    def run(): Unit = {
      while (streamIterator.hasNext) {
        val next = streamIterator.next()
        store(next)
      }
    }
  }

  override def onStart(): Unit = {
    new Thread(new ReadAndStore).run()    
  }

  override def onStop(): Unit = { }
}

Answer 2

Slightly modified code tat works with Spark 2.0:

import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.StreamingContext
import org.apache.spark.streaming.dstream.ReceiverInputDStream
import org.apache.spark.streaming.receiver.Receiver
import scala.reflect.ClassTag

class InfiniteDStream[T: ClassTag](
                                    @transient ssc_ : StreamingContext,
                                    stream: Stream[T],
                                    storageLevel: StorageLevel
                                  ) extends ReceiverInputDStream[T](ssc_) {

  override def getReceiver(): Receiver[T] = {
    new InfiniteStreamReceiver(stream, storageLevel)
  }
}

class InfiniteStreamReceiver[T](stream: Stream[T], storageLevel: StorageLevel) extends Receiver[T](storageLevel) {

  private class ReadAndStore extends Runnable {
    def run(): Unit = {
      stream.foreach(store)
    }
  }

  override def onStart(): Unit = {
    val t = new Thread(new ReadAndStore)
    t.setDaemon(true)
    t.run()
  }

  override def onStop(): Unit = {}
}