[SPARK-10071] [STREAMING] Output a warning when writing QueueInputDStream and throw a better exception when reading QueueInputDStream

Output a warning when serializing QueueInputDStream rather than throwing an exception to allow unit tests use it. Moreover, this PR also throws an better exception when deserializing QueueInputDStream to make the user find out the problem easily. The previous exception is hard to understand: https://issues.apache.org/jira/browse/SPARK-8553

Author: zsxwing <zsxwing@gmail.com>

Closes apache#8624 from zsxwing/SPARK-10071 and squashes the following commits:

847cfa8 [zsxwing] Output a warning when writing QueueInputDStream and throw a better exception when reading QueueInputDStream

Author: zsxwing

streaming/src/main/scala/org/apache/spark/streaming/Checkpoint.scala

@@ -321,7 +321,7 @@ object CheckpointReader extends Logging {
 
     // Try to read the checkpoint files in the order
     logInfo("Checkpoint files found: " + checkpointFiles.mkString(","))
-    val compressionCodec = CompressionCodec.createCodec(conf)
+    var readError: Exception = null
     checkpointFiles.foreach(file => {
       logInfo("Attempting to load checkpoint from file " + file)
       try {
@@ -332,13 +332,15 @@ object CheckpointReader extends Logging {
         return Some(cp)
       } catch {
         case e: Exception =>
+          readError = e
           logWarning("Error reading checkpoint from file " + file, e)
       }
     })
 
     // If none of checkpoint files could be read, then throw exception
     if (!ignoreReadError) {
-      throw new SparkException(s"Failed to read checkpoint from directory $checkpointPath")
+      throw new SparkException(
+        s"Failed to read checkpoint from directory $checkpointPath", readError)
     }
     None
   }

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

@@ -17,7 +17,7 @@
 
 package org.apache.spark.streaming.dstream
 
-import java.io.{NotSerializableException, ObjectOutputStream}
+import java.io.{NotSerializableException, ObjectInputStream, ObjectOutputStream}
 
 import scala.collection.mutable.{ArrayBuffer, Queue}
 import scala.reflect.ClassTag
@@ -37,8 +37,13 @@ class QueueInputDStream[T: ClassTag](
 
   override def stop() { }
 
+  private def readObject(in: ObjectInputStream): Unit = {
+    throw new NotSerializableException("queueStream doesn't support checkpointing. " +
+      "Please don't use queueStream when checkpointing is enabled.")
+  }
+
   private def writeObject(oos: ObjectOutputStream): Unit = {
-    throw new NotSerializableException("queueStream doesn't support checkpointing")
+    logWarning("queueStream doesn't support checkpointing")
   }
 
   override def compute(validTime: Time): Option[RDD[T]] = {

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

@@ -30,7 +30,7 @@ import org.scalatest.concurrent.Timeouts
 import org.scalatest.exceptions.TestFailedDueToTimeoutException
 import org.scalatest.time.SpanSugar._
 
-import org.apache.spark.{Logging, SparkConf, SparkContext, SparkFunSuite}
+import org.apache.spark._
 import org.apache.spark.metrics.MetricsSystem
 import org.apache.spark.metrics.source.Source
 import org.apache.spark.storage.StorageLevel
@@ -726,16 +726,26 @@ class StreamingContextSuite extends SparkFunSuite with BeforeAndAfter with Timeo
   }
 
   test("queueStream doesn't support checkpointing") {
-    val checkpointDir = Utils.createTempDir()
-    ssc = new StreamingContext(master, appName, batchDuration)
-    val rdd = ssc.sparkContext.parallelize(1 to 10)
-    ssc.queueStream[Int](Queue(rdd)).print()
-    ssc.checkpoint(checkpointDir.getAbsolutePath)
-    val e = intercept[NotSerializableException] {
-      ssc.start()
+    val checkpointDirectory = Utils.createTempDir().getAbsolutePath()
+    def creatingFunction(): StreamingContext = {
+      val _ssc = new StreamingContext(conf, batchDuration)
+      val rdd = _ssc.sparkContext.parallelize(1 to 10)
+      _ssc.checkpoint(checkpointDirectory)
+      _ssc.queueStream[Int](Queue(rdd)).register()
+      _ssc
+    }
+    ssc = StreamingContext.getOrCreate(checkpointDirectory, creatingFunction _)
+    ssc.start()
+    eventually(timeout(10000 millis)) {
+      assert(Checkpoint.getCheckpointFiles(checkpointDirectory).size > 1)
+    }
+    ssc.stop()
+    val e = intercept[SparkException] {
+      ssc = StreamingContext.getOrCreate(checkpointDirectory, creatingFunction _)
     }
     // StreamingContext.validate changes the message, so use "contains" here
-    assert(e.getMessage.contains("queueStream doesn't support checkpointing"))
+    assert(e.getCause.getMessage.contains("queueStream doesn't support checkpointing. " +
+      "Please don't use queueStream when checkpointing is enabled."))
   }
 
   def addInputStream(s: StreamingContext): DStream[Int] = {