Merge pull request apache#43 in BDP/apache-spark from fix_threadpool_metric to netflix/2.1.1-unstable

Squashed commit of the following:

commit 9f19629b14cb9823c0115399a43a8116efbe1145
Author: Davis Shepherd <[email protected]>
Date:   Wed Sep 19 12:20:22 2018 -0700

    NETFLIX-BUILD: Expose largest threadPool size in executor metrics

Author: dgshep

core/src/main/scala/org/apache/spark/executor/ExecutorSource.scala

@@ -58,12 +58,17 @@ class ExecutorSource(threadPool: ThreadPoolExecutor, executorId: String) extends
     override def getValue: Int = threadPool.getPoolSize()
   })
 
-  // Gauge got executor thread pool's largest number of threads that have ever simultaneously
-  // been in th pool
+  // Gauge for executor thread pool's maximum allowed number of threads
   metricRegistry.register(MetricRegistry.name("threadpool", "maxPool_size"), new Gauge[Int] {
     override def getValue: Int = threadPool.getMaximumPoolSize()
   })
 
+  // Gauge for executor thread pool's largest number of threads that have ever simultaneously
+  // been in the pool
+  metricRegistry.register(MetricRegistry.name("threadpool", "largestPool_size"), new Gauge[Int] {
+    override def getValue: Int = threadPool.getLargestPoolSize()
+  })
+
   // Gauge for file system stats of this executor
   for (scheme <- Array("hdfs", "file")) {
     registerFileSystemStat(scheme, "read_bytes", _.getBytesRead(), 0L)