SPARK-1124: Fix infinite retries of reduce stage when a map stage failed

In the previous code, if you had a failing map stage and then tried to
run reduce stages on it repeatedly, the first reduce stage would fail
correctly, but the later ones would mistakenly believe that all map
outputs are available and start failing infinitely with fetch failures
from "null".

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

@@ -272,8 +272,10 @@ class DAGScheduler(
     if (mapOutputTracker.has(shuffleDep.shuffleId)) {
       val serLocs = mapOutputTracker.getSerializedMapOutputStatuses(shuffleDep.shuffleId)
       val locs = MapOutputTracker.deserializeMapStatuses(serLocs)
-      for (i <- 0 until locs.size) stage.outputLocs(i) = List(locs(i))
-      stage.numAvailableOutputs = locs.size
+      for (i <- 0 until locs.size) {
+        stage.outputLocs(i) = Option(locs(i)).toList   // locs(i) will be null if missing
+      }
+      stage.numAvailableOutputs = locs.count(_ != null)
     } else {
       // Kind of ugly: need to register RDDs with the cache and map output tracker here
       // since we can't do it in the RDD constructor because # of partitions is unknown
@@ -373,25 +375,26 @@ class DAGScheduler(
           } else {
             def removeStage(stageId: Int) {
               // data structures based on Stage
-              stageIdToStage.get(stageId).foreach { s =>
-                if (running.contains(s)) {
+              for (stage <- stageIdToStage.get(stageId)) {
+                if (running.contains(stage)) {
                   logDebug("Removing running stage %d".format(stageId))
-                  running -= s
+                  running -= stage
+                }
+                stageToInfos -= stage
+                for (shuffleDep <- stage.shuffleDep) {
+                  shuffleToMapStage.remove(shuffleDep.shuffleId)
                 }
-                stageToInfos -= s
-                shuffleToMapStage.keys.filter(shuffleToMapStage(_) == s).foreach(shuffleId =>
-                  shuffleToMapStage.remove(shuffleId))
-                if (pendingTasks.contains(s) && !pendingTasks(s).isEmpty) {
+                if (pendingTasks.contains(stage) && !pendingTasks(stage).isEmpty) {
                   logDebug("Removing pending status for stage %d".format(stageId))
                 }
-                pendingTasks -= s
-                if (waiting.contains(s)) {
+                pendingTasks -= stage
+                if (waiting.contains(stage)) {
                   logDebug("Removing stage %d from waiting set.".format(stageId))
-                  waiting -= s
+                  waiting -= stage
                 }
-                if (failed.contains(s)) {
+                if (failed.contains(stage)) {
                   logDebug("Removing stage %d from failed set.".format(stageId))
-                  failed -= s
+                  failed -= stage
                 }
               }
               // data structures based on StageId

core/src/test/scala/org/apache/spark/FailureSuite.scala

@@ -81,6 +81,19 @@ class FailureSuite extends FunSuite with LocalSparkContext {
     FailureSuiteState.clear()
   }
 
+  // Run a map-reduce job in which the map stage always fails.
+  test("failure in a map stage") {
+    sc = new SparkContext("local", "test")
+    val data = sc.makeRDD(1 to 3).map(x => { throw new Exception; (x, x) }).groupByKey(3)
+    intercept[SparkException] {
+      data.collect()
+    }
+    // Make sure that running new jobs with the same map stage also fails
+    intercept[SparkException] {
+      data.collect()
+    }
+  }
+
   test("failure because task results are not serializable") {
     sc = new SparkContext("local[1,1]", "test")
     val results = sc.makeRDD(1 to 3).map(x => new NonSerializable)