[SPARK-7318] [STREAMING] DStream cleans objects that are not closures

I added a check in `ClosureCleaner#clean` to fail fast if this is detected in the future. tdas

Author: Andrew Or <andrew@databricks.com>

Closes #5860 from andrewor14/streaming-closure-cleaner and squashes the following commits:

8e971d7 [Andrew Or] Do not throw exception if object to clean is not closure
5ee4e25 [Andrew Or] Fix tests
eed3390 [Andrew Or] Merge branch 'master' of github.com:apache/spark into streaming-closure-cleaner
67eeff4 [Andrew Or] Add tests
a4fa768 [Andrew Or] Clean the closure, not the RDD

core/src/main/scala/org/apache/spark/util/ClosureCleaner.scala

@@ -179,6 +179,11 @@ private[spark] object ClosureCleaner extends Logging {
       cleanTransitively: Boolean,
       accessedFields: Map[Class[_], Set[String]]): Unit = {
 
+    if (!isClosure(func.getClass)) {
+      logWarning("Expected a closure; got " + func.getClass.getName)
+      return
+    }
+
     // TODO: clean all inner closures first. This requires us to find the inner objects.
     // TODO: cache outerClasses / innerClasses / accessedFields
 

streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala

@@ -553,7 +553,8 @@ abstract class DStream[T: ClassTag] (
     // because the DStream is reachable from the outer object here, and because 
     // DStreams can't be serialized with closures, we can't proactively check 
     // it for serializability and so we pass the optional false to SparkContext.clean
-    transform((r: RDD[T], t: Time) => context.sparkContext.clean(transformFunc(r), false))
+    val cleanedF = context.sparkContext.clean(transformFunc, false)
+    transform((r: RDD[T], t: Time) => cleanedF(r))
   }
 
   /**

streaming/src/test/scala/org/apache/spark/streaming/ReceiverSuite.scala

@@ -256,8 +256,8 @@ class ReceiverSuite extends TestSuiteBase with Timeouts with Serializable {
     }
 
     withStreamingContext(new StreamingContext(sparkConf, batchDuration)) { ssc =>
-      val receiver1 = ssc.sparkContext.clean(new FakeReceiver(sendData = true))
-      val receiver2 = ssc.sparkContext.clean(new FakeReceiver(sendData = true))
+      val receiver1 = new FakeReceiver(sendData = true)
+      val receiver2 = new FakeReceiver(sendData = true)
       val receiverStream1 = ssc.receiverStream(receiver1)
       val receiverStream2 = ssc.receiverStream(receiver2)
       receiverStream1.register()