Consider the number of selector too

core/src/main/scala/org/apache/spark/ui/JettyUtils.scala

@@ -270,19 +270,25 @@ private[spark] object JettyUtils extends Logging {
 
       gzipHandlers.foreach(collection.addHandler)
       connectors.foreach(_.setHost(hostName))
-      // As each Acceptor will use one thread, the number of threads should at least be the number
-      // of acceptors plus 1. (See SPARK-13776)
+      // As each acceptor and each selector will use one thread, the number of threads should at
+      // least be the number of acceptors and selectors plus 1. (See SPARK-13776)
       var minThreads = 1
-      connectors.collect { case c: AbstractConnector => c }.foreach { c =>
+      connectors.foreach { c =>
+        // Currently we only use "SelectChannelConnector"
+        val connector = c.asInstanceOf[SelectChannelConnector]
         // Limit the max acceptor number to 8 so that we don't waste a lot of threads
-        c.setAcceptors(Math.min(c.getAcceptors, 8))
-        minThreads += c.getAcceptors
+        connector.setAcceptors(math.min(connector.getAcceptors, 8))
+        // The number of selectors always equals to the number of acceptors
+        minThreads += connector.getAcceptors * 2
       }
       server.setConnectors(connectors.toArray)
 
       val pool = new QueuedThreadPool
-      pool.setMaxThreads(Math.max(pool.getMaxThreads, minThreads))
-      pool.setMinThreads(Math.min(pool.getMinThreads, pool.getMaxThreads))
+      if (serverName.nonEmpty) {
+        pool.setName(serverName)
+      }
+      pool.setMaxThreads(math.max(pool.getMaxThreads, minThreads))
+      pool.setMinThreads(math.min(pool.getMinThreads, pool.getMaxThreads))
       pool.setDaemon(true)
       server.setThreadPool(pool)
       val errorHandler = new ErrorHandler()

core/src/main/scala/org/apache/spark/ui/WebUI.scala

@@ -134,7 +134,7 @@ private[spark] abstract class WebUI(
   def bind() {
     assert(!serverInfo.isDefined, "Attempted to bind %s more than once!".format(className))
     try {
-      var host = Option(conf.getenv("SPARK_LOCAL_IP")).getOrElse("0.0.0.0")
+      val host = Option(conf.getenv("SPARK_LOCAL_IP")).getOrElse("0.0.0.0")
       serverInfo = Some(startJettyServer(host, port, sslOptions, handlers, conf, name))
       logInfo("Bound %s to %s, and started at http://%s:%d".format(className, host,
         publicHostName, boundPort))