[SPARK-9126] [MLLIB] do not assert on time taken by Thread.sleep()

Measure lower and upper bounds for task time and use them for validation. This PR also implements `Stopwatch.toString`. This suite should finish in less than 1 second.

jkbradley pwendell

Author: Xiangrui Meng <meng@databricks.com>

Closes #7457 from mengxr/SPARK-9126 and squashes the following commits:

4b40faa [Xiangrui Meng] simplify tests
739f5bd [Xiangrui Meng] do not assert on time taken by Thread.sleep()

1 files changed, 3 insertions, 1 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala b/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
index 5fdf878a3d..8d4174124b 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
@@ -67,6 +67,8 @@ private[spark] abstract class Stopwatch extends Serializable {
    */
   def elapsed(): Long
 
+  override def toString: String = s"$name: ${elapsed()}ms"
+
   /**
    * Gets the current time in milliseconds.
    */
@@ -145,7 +147,7 @@ private[spark] class MultiStopwatch(@transient private val sc: SparkContext) ext
 
   override def toString: String = {
     stopwatches.values.toArray.sortBy(_.name)
-      .map(c => s"  ${c.name}: ${c.elapsed()}ms")
+      .map(c => s"  $c")
       .mkString("{\n", ",\n", "\n}")
   }
 }