Fix reference bug in Kryo serializer, add test, update version

core/src/main/scala/spark/KryoSerializer.scala

@@ -157,27 +157,34 @@ class KryoSerializer extends spark.serializer.Serializer with Logging {
 
     // Register maps with a special serializer since they have complex internal structure
     class ScalaMapSerializer(buildMap: Array[(Any, Any)] => scala.collection.Map[Any, Any])
-    extends KSerializer[Array[(Any, Any)] => scala.collection.Map[Any, Any]] {
+      extends KSerializer[Array[(Any, Any)] => scala.collection.Map[Any, Any]] {
+
+      //hack, look at https://groups.google.com/forum/#!msg/kryo-users/Eu5V4bxCfws/k-8UQ22y59AJ
+      private final val FAKE_REFERENCE = new Object()
       override def write(
-        kryo: Kryo,
-        output: KryoOutput,
-        obj: Array[(Any, Any)] => scala.collection.Map[Any, Any]) {
+                          kryo: Kryo,
+                          output: KryoOutput,
+                          obj: Array[(Any, Any)] => scala.collection.Map[Any, Any]) {
         val map = obj.asInstanceOf[scala.collection.Map[Any, Any]]
-        kryo.writeObject(output, map.size.asInstanceOf[java.lang.Integer])
+        output.writeInt(map.size)
         for ((k, v) <- map) {
           kryo.writeClassAndObject(output, k)
           kryo.writeClassAndObject(output, v)
         }
       }
       override def read (
-        kryo: Kryo,
-        input: KryoInput,
-        cls: Class[Array[(Any, Any)] => scala.collection.Map[Any, Any]])
+                          kryo: Kryo,
+                          input: KryoInput,
+                          cls: Class[Array[(Any, Any)] => scala.collection.Map[Any, Any]])
       : Array[(Any, Any)] => scala.collection.Map[Any, Any] = {
-        val size = kryo.readObject(input, classOf[java.lang.Integer]).intValue
+        kryo.reference(FAKE_REFERENCE)
+        val size = input.readInt()
         val elems = new Array[(Any, Any)](size)
-        for (i <- 0 until size)
-          elems(i) = (kryo.readClassAndObject(input), kryo.readClassAndObject(input))
+        for (i <- 0 until size) {
+          val k = kryo.readClassAndObject(input)
+          val v = kryo.readClassAndObject(input)
+          elems(i)=(k,v)
+        }
         buildMap(elems).asInstanceOf[Array[(Any, Any)] => scala.collection.Map[Any, Any]]
       }
     }

core/src/test/scala/spark/KryoSerializerSuite.scala

@@ -82,6 +82,7 @@ class KryoSerializerSuite extends FunSuite {
     check(mutable.HashMap(1 -> "one", 2 -> "two"))
     check(mutable.HashMap("one" -> 1, "two" -> 2))
     check(List(Some(mutable.HashMap(1->1, 2->2)), None, Some(mutable.HashMap(3->4))))
+    check(List(mutable.HashMap("one" -> 1, "two" -> 2),mutable.HashMap(1->"one",2->"two",3->"three")))
   }
 
   test("custom registrator") {

project/SparkBuild.scala

@@ -132,7 +132,7 @@ object SparkBuild extends Build {
       "org.apache.hadoop" % "hadoop-core" % HADOOP_VERSION,
       "asm" % "asm-all" % "3.3.1",
       "com.google.protobuf" % "protobuf-java" % "2.4.1",
-      "de.javakaffee" % "kryo-serializers" % "0.20",
+      "de.javakaffee" % "kryo-serializers" % "0.22",
       "com.typesafe.akka" % "akka-actor" % "2.0.3",
       "com.typesafe.akka" % "akka-remote" % "2.0.3",
       "com.typesafe.akka" % "akka-slf4j" % "2.0.3",