Use Java 8 compatible way to get pid

Author: dongjoon-hyun

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

@@ -2289,7 +2289,8 @@ private[spark] object Utils extends Logging with SparkClassUtils {
 
  /** Return a heap dump. Used to capture dumps for the web UI */
  def getHeapHistogram(): Array[String] = {
- val pid = String.valueOf(ProcessHandle.current().pid())
+ // From Java 9+, we can use 'ProcessHandle.current().pid()'
+ val pid = getProcessName().split("@").head
  val builder = new ProcessBuilder("jmap", "-histo:live", pid)
  builder.redirectErrorStream(true)
  val p = builder.start()