Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/2940#discussion_r19509599
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala
---
@@ -0,0 +1,144 @@
+package org.apache.spark.streaming.receiver
+
+import java.nio.ByteBuffer
+
+import scala.collection.mutable.ArrayBuffer
+import scala.concurrent.{Await, ExecutionContext, Future}
+import scala.concurrent.duration._
+import scala.language.{existentials, postfixOps}
+
+import WriteAheadLogBasedBlockHandler._
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.Path
+import org.apache.spark.{SparkException, Logging, SparkConf}
+import org.apache.spark.storage.{BlockManager, StorageLevel, StreamBlockId}
+import org.apache.spark.streaming.util.{Clock, SystemClock,
WriteAheadLogManager}
+import org.apache.spark.util.Utils
+
+private[streaming] sealed trait ReceivedBlock
+private[streaming] case class ArrayBufferBlock(arrayBuffer:
ArrayBuffer[_]) extends ReceivedBlock
+private[streaming] case class IteratorBlock(iterator: Iterator[_]) extends
ReceivedBlock
+private[streaming] case class ByteBufferBlock(byteBuffer: ByteBuffer)
extends ReceivedBlock
+
+
+/** Trait that represents a class that handles the storage of blocks
received by receiver */
+private[streaming] trait ReceivedBlockHandler {
+
+ /** Store a received block with the given block id */
+ def storeBlock(blockId: StreamBlockId, receivedBlock: ReceivedBlock):
Option[AnyRef]
--- End diff --
I played with the typed traits, and realized that it doesnt help much. Here
the points to note.
- Which implementation of ReceivedBlockHandler will be created is not known
at compile time (depends on runtime settings).
- Users of this ReceivedBlockHandler (that is, ReceiverSupervisor) should
treat the metadata returned by ReceivedBlockHandler.storeBlock() as a black box
(so as a AnyRef or Any), and not have any implementation specific logic to keep
things simple.
Hence, having type in the trait and returning specific type in each
implementation is kind of moot, and downstream code will treat is as AnyRef or
Any. Rather it introduces weirdness in some places. Ex. default implementation
BlockManagerBasedBlockHandler.storeBlock always return None and hence does not
really need a type.
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