[SPARK-8880] Fix confusing Stage.attemptId member variable

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #7275 from kayousterhout/SPARK-8880 and squashes the following commits:

3e9ce7c [Kay Ousterhout] Added missing return type
e150278 [Kay Ousterhout] [SPARK-8880] Fix confusing Stage.attemptId member variable

core/src/main/scala/org/apache/spark/scheduler/DAGScheduler.scala

@@ -872,7 +872,7 @@ class DAGScheduler(
     // serializable. If tasks are not serializable, a SparkListenerStageCompleted event
     // will be posted, which should always come after a corresponding SparkListenerStageSubmitted
     // event.
-    stage.latestInfo = StageInfo.fromStage(stage, Some(partitionsToCompute.size))
+    stage.makeNewStageAttempt(partitionsToCompute.size)
     outputCommitCoordinator.stageStart(stage.id)
     listenerBus.post(SparkListenerStageSubmitted(stage.latestInfo, properties))
 
@@ -937,8 +937,8 @@ class DAGScheduler(
       logInfo("Submitting " + tasks.size + " missing tasks from " + stage + " (" + stage.rdd + ")")
       stage.pendingTasks ++= tasks
       logDebug("New pending tasks: " + stage.pendingTasks)
-      taskScheduler.submitTasks(
-        new TaskSet(tasks.toArray, stage.id, stage.newAttemptId(), stage.firstJobId, properties))
+      taskScheduler.submitTasks(new TaskSet(
+        tasks.toArray, stage.id, stage.latestInfo.attemptId, stage.firstJobId, properties))
       stage.latestInfo.submissionTime = Some(clock.getTimeMillis())
     } else {
       // Because we posted SparkListenerStageSubmitted earlier, we should mark

core/src/main/scala/org/apache/spark/scheduler/Stage.scala

@@ -62,22 +62,28 @@ private[spark] abstract class Stage(
 
   var pendingTasks = new HashSet[Task[_]]
 
+  /** The ID to use for the next new attempt for this stage. */
   private var nextAttemptId: Int = 0
 
   val name = callSite.shortForm
   val details = callSite.longForm
 
-  /** Pointer to the latest [StageInfo] object, set by DAGScheduler. */
-  var latestInfo: StageInfo = StageInfo.fromStage(this)
+  /**
+   * Pointer to the [StageInfo] object for the most recent attempt. This needs to be initialized
+   * here, before any attempts have actually been created, because the DAGScheduler uses this
+   * StageInfo to tell SparkListeners when a job starts (which happens before any stage attempts
+   * have been created).
+   */
+  private var _latestInfo: StageInfo = StageInfo.fromStage(this, nextAttemptId)
 
-  /** Return a new attempt id, starting with 0. */
-  def newAttemptId(): Int = {
-    val id = nextAttemptId
+  /** Creates a new attempt for this stage by creating a new StageInfo with a new attempt ID. */
+  def makeNewStageAttempt(numPartitionsToCompute: Int): Unit = {
+    _latestInfo = StageInfo.fromStage(this, nextAttemptId, Some(numPartitionsToCompute))
     nextAttemptId += 1
-    id
   }
 
-  def attemptId: Int = nextAttemptId
+  /** Returns the StageInfo for the most recent attempt for this stage. */
+  def latestInfo: StageInfo = _latestInfo
 
   override final def hashCode(): Int = id
   override final def equals(other: Any): Boolean = other match {

core/src/main/scala/org/apache/spark/scheduler/StageInfo.scala

@@ -70,12 +70,12 @@ private[spark] object StageInfo {
    * shuffle dependencies. Therefore, all ancestor RDDs related to this Stage's RDD through a
    * sequence of narrow dependencies should also be associated with this Stage.
    */
-  def fromStage(stage: Stage, numTasks: Option[Int] = None): StageInfo = {
+  def fromStage(stage: Stage, attemptId: Int, numTasks: Option[Int] = None): StageInfo = {
     val ancestorRddInfos = stage.rdd.getNarrowAncestors.map(RDDInfo.fromRdd)
     val rddInfos = Seq(RDDInfo.fromRdd(stage.rdd)) ++ ancestorRddInfos
     new StageInfo(
       stage.id,
-      stage.attemptId,
+      attemptId,
       stage.name,
       numTasks.getOrElse(stage.numTasks),
       rddInfos,