clear sqlListener

Author: carsonwang

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -1217,6 +1217,7 @@ class SQLContext private[sql](
   sparkContext.addSparkListener(new SparkListener {
     override def onApplicationEnd(applicationEnd: SparkListenerApplicationEnd): Unit = {
       SQLContext.clearInstantiatedContext(self)
+      SQLContext.clearSqlListener()
     }
   })
 

sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLListenerSuite.scala

@@ -343,6 +343,7 @@ class SQLListenerMemoryLeakSuite extends SparkFunSuite {
       .set("spark.sql.ui.retainedExecutions", "50") // Set it to 50 to run this test quickly
     val sc = new SparkContext(conf)
     try {
+      SQLContext.clearSqlListener()
       val sqlContext = new SQLContext(sc)
       import sqlContext.implicits._
       // Run 100 successful executions and 100 failed executions.