SPARK-5217 Spark UI should report pending stages during job execution on AllStagesPage.

![screenshot from 2015-01-16 13 43 25](https://cloud.githubusercontent.com/assets/992952/5773256/d61df300-9d85-11e4-9b5a-6730058839fa.png)

This is a first step towards having time remaining estimates for queued and running jobs. See SPARK-5216

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #4043 from ScrapCodes/SPARK-5216/5217-show-waiting-stages and squashes the following commits:

3b11803 [Prashant Sharma] Review feedback.
0992842 [Prashant Sharma] Switched to Linked hashmap, changed the order to active->pending->completed->failed. And changed pending stages to not reverse sort.
c19d82a [Prashant Sharma] SPARK-5217 Spark UI should report pending stages during job execution on AllStagesPage.

core/src/main/scala/org/apache/spark/ui/jobs/AllStagesPage.scala

@@ -33,6 +33,7 @@ private[ui] class AllStagesPage(parent: StagesTab) extends WebUIPage("") {
   def render(request: HttpServletRequest): Seq[Node] = {
     listener.synchronized {
       val activeStages = listener.activeStages.values.toSeq
+      val pendingStages = listener.pendingStages.values.toSeq
       val completedStages = listener.completedStages.reverse.toSeq
       val numCompletedStages = listener.numCompletedStages
       val failedStages = listener.failedStages.reverse.toSeq
@@ -43,6 +44,10 @@ private[ui] class AllStagesPage(parent: StagesTab) extends WebUIPage("") {
         new StageTableBase(activeStages.sortBy(_.submissionTime).reverse,
           parent.basePath, parent.listener, isFairScheduler = parent.isFairScheduler,
           killEnabled = parent.killEnabled)
+      val pendingStagesTable =
+        new StageTableBase(pendingStages.sortBy(_.submissionTime).reverse,
+          parent.basePath, parent.listener, isFairScheduler = parent.isFairScheduler,
+          killEnabled = false)
       val completedStagesTable =
         new StageTableBase(completedStages.sortBy(_.submissionTime).reverse, parent.basePath,
           parent.listener, isFairScheduler = parent.isFairScheduler, killEnabled = false)
@@ -72,6 +77,10 @@ private[ui] class AllStagesPage(parent: StagesTab) extends WebUIPage("") {
               <a href="#active"><strong>Active Stages:</strong></a>
               {activeStages.size}
             </li>
+            <li>
+              <a href="#pending"><strong>Pending Stages:</strong></a>
+              {pendingStages.size}
+            </li>
             <li>
               <a href="#completed"><strong>Completed Stages:</strong></a>
               {numCompletedStages}
@@ -91,6 +100,8 @@ private[ui] class AllStagesPage(parent: StagesTab) extends WebUIPage("") {
         }} ++
         <h4 id="active">Active Stages ({activeStages.size})</h4> ++
         activeStagesTable.toNodeSeq ++
+        <h4 id="pending">Pending Stages ({pendingStages.size})</h4> ++
+        pendingStagesTable.toNodeSeq ++
         <h4 id="completed">Completed Stages ({numCompletedStages})</h4> ++
         completedStagesTable.toNodeSeq ++
         <h4 id ="failed">Failed Stages ({numFailedStages})</h4> ++

core/src/main/scala/org/apache/spark/ui/jobs/JobProgressListener.scala

@@ -56,6 +56,7 @@ class JobProgressListener(conf: SparkConf) extends SparkListener with Logging {
   val jobIdToData = new HashMap[JobId, JobUIData]
 
   // Stages:
+  val pendingStages = new HashMap[StageId, StageInfo]
   val activeStages = new HashMap[StageId, StageInfo]
   val completedStages = ListBuffer[StageInfo]()
   val skippedStages = ListBuffer[StageInfo]()
@@ -157,6 +158,7 @@ class JobProgressListener(conf: SparkConf) extends SparkListener with Logging {
         stageIds = jobStart.stageIds,
         jobGroup = jobGroup,
         status = JobExecutionStatus.RUNNING)
+    jobStart.stageInfos.foreach(x => pendingStages(x.stageId) = x)
     // Compute (a potential underestimate of) the number of tasks that will be run by this job.
     // This may be an underestimate because the job start event references all of the result
     // stages' transitive stage dependencies, but some of these stages might be skipped if their
@@ -187,6 +189,7 @@ class JobProgressListener(conf: SparkConf) extends SparkListener with Logging {
     }
     jobData.completionTime = Option(jobEnd.time).filter(_ >= 0)
 
+    jobData.stageIds.foreach(pendingStages.remove)
     jobEnd.jobResult match {
       case JobSucceeded =>
         completedJobs += jobData
@@ -257,7 +260,7 @@ class JobProgressListener(conf: SparkConf) extends SparkListener with Logging {
   override def onStageSubmitted(stageSubmitted: SparkListenerStageSubmitted) = synchronized {
     val stage = stageSubmitted.stageInfo
     activeStages(stage.stageId) = stage
-
+    pendingStages.remove(stage.stageId)
     val poolName = Option(stageSubmitted.properties).map {
       p => p.getProperty("spark.scheduler.pool", DEFAULT_POOL_NAME)
     }.getOrElse(DEFAULT_POOL_NAME)