spark git commit: [SPARK-5035] [Streaming] ReceiverMessage trait should extend Serializable

[td...@apache.org]

Repository: spark
Updated Branches:
  refs/heads/master c4f0b4f33 -> fe6efacc0


[SPARK-5035] [Streaming] ReceiverMessage trait should extend Serializable

Spark Streaming's ReceiverMessage trait should extend Serializable in order to fix a subtle bug that only occurs when running on a real cluster:

If you attempt to send a fire-and-forget message to a remote Akka actor and that message cannot be serialized, then this seems to lead to more-or-less silent failures. As an optimization, Akka skips message serialization for messages sent within the same JVM. As a result, Spark's unit tests will never fail due to non-serializable Akka messages, but these will cause mostly-silent failures when running on a real cluster.

Before this patch, here was the code for ReceiverMessage:

```
/** Messages sent to the NetworkReceiver. */
private[streaming] sealed trait ReceiverMessage
private[streaming] object StopReceiver extends ReceiverMessage
```

Since ReceiverMessage does not extend Serializable and StopReceiver is a regular `object`, not a `case object`, StopReceiver will throw serialization errors. As a result, graceful receiver shutdown is broken on real clusters (and local-cluster mode) but works in local modes. If you want to reproduce this, try running the word count example from the Streaming Programming Guide in the Spark shell:

```
import org.apache.spark._
import org.apache.spark.streaming._
import org.apache.spark.streaming.StreamingContext._
val ssc = new StreamingContext(sc, Seconds(10))
// Create a DStream that will connect to hostname:port, like localhost:9999
val lines = ssc.socketTextStream("localhost", 9999)
// Split each line into words
val words = lines.flatMap(_.split(" "))
import org.apache.spark.streaming.StreamingContext._
// Count each word in each batch
val pairs = words.map(word => (word, 1))
val wordCounts = pairs.reduceByKey(_ + _)
// Print the first ten elements of each RDD generated in this DStream to the console
wordCounts.print()
ssc.start()
Thread.sleep(10000)
ssc.stop(true, true)
```

Prior to this patch, this would work correctly in local mode but fail when running against a real cluster (it would report that some receivers were not shut down).

Author: Josh Rosen <jo...@databricks.com>

Closes #3857 from JoshRosen/SPARK-5035 and squashes the following commits:

71d0eae [Josh Rosen] [SPARK-5035] ReceiverMessage trait should extend Serializable.


Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/fe6efacc
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/fe6efacc
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/fe6efacc

Branch: refs/heads/master
Commit: fe6efacc0b865e9e827a1565877077000e63976e
Parents: c4f0b4f
Author: Josh Rosen <jo...@databricks.com>
Authored: Wed Dec 31 16:02:47 2014 -0800
Committer: Tathagata Das <ta...@gmail.com>
Committed: Wed Dec 31 16:02:47 2014 -0800

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 .../org/apache/spark/streaming/receiver/ReceiverMessage.scala      | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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http://git-wip-us.apache.org/repos/asf/spark/blob/fe6efacc/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverMessage.scala
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diff --git a/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverMessage.scala b/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverMessage.scala
index bf39d1e..ab9fa19 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverMessage.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceiverMessage.scala
@@ -18,6 +18,6 @@
 package org.apache.spark.streaming.receiver
 
 /** Messages sent to the NetworkReceiver. */
-private[streaming] sealed trait ReceiverMessage
+private[streaming] sealed trait ReceiverMessage extends Serializable
 private[streaming] object StopReceiver extends ReceiverMessage
 


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