[SPARK-20134][SQL] SQLMetrics.postDriverMetricUpdates to simplify driver side metric updates

## What changes were proposed in this pull request?
It is not super intuitive how to update SQLMetric on the driver side. This patch introduces a new SQLMetrics.postDriverMetricUpdates function to do that, and adds documentation to make it more obvious.

## How was this patch tested?
Updated a test case to use this method.

Author: Reynold Xin <rxin@databricks.com>

Closes #17464 from rxin/SPARK-20134.

1 files changed, 5 insertions, 3 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLListenerSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLListenerSuite.scala
index e41c00ecec..e6cd41e4fa 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLListenerSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLListenerSuite.scala
@@ -477,9 +477,11 @@ private case class MyPlan(sc: SparkContext, expectedValue: Long) extends LeafExe
 
   override def doExecute(): RDD[InternalRow] = {
     longMetric("dummy") += expectedValue
-    sc.listenerBus.post(SparkListenerDriverAccumUpdates(
-      sc.getLocalProperty(SQLExecution.EXECUTION_ID_KEY).toLong,
-      metrics.values.map(m => m.id -> m.value).toSeq))
+
+    SQLMetrics.postDriverMetricUpdates(
+      sc,
+      sc.getLocalProperty(SQLExecution.EXECUTION_ID_KEY),
+      metrics.values.toSeq)
     sc.emptyRDD
   }
 }