Merge pull request apache-spark-on-k8s#343 from jeremyjliu/jl/expose-r-backend

Move RBackend to member variable

Author: amenck

core/src/main/scala/org/apache/spark/deploy/RRunner.scala

@@ -40,6 +40,8 @@ import org.apache.spark.util.RedirectThread
  * subprocess and then has it connect back to the JVM to access system properties etc.
  */
 object RRunner extends CondaRunner with Logging {
+  val sparkRBackend = new RBackend()
+
   override def run(args: Array[String], maybeConda: Option[CondaEnvironment]): Unit = {
     val rFile = PythonRunner.formatPath(args(0))
 
@@ -84,7 +86,6 @@ object RRunner extends CondaRunner with Logging {
 
     // Launch a SparkR backend server for the R process to connect to; this will let it see our
     // Java system properties etc.
-    val sparkRBackend = new RBackend()
     @volatile var sparkRBackendPort = 0
     val initialized = new Semaphore(0)
     val sparkRBackendThread = new Thread("SparkR backend") {