apache/spark — pull request #429 by scwf (2014-04-16 16:01:23+00:00)
Title: [SPARK-1361] DAGScheduler throws NullPointerException occasionally

this is an order issue of construction and starting of the taskScheduler and the dagScheduler in SparkContext. now taskScheduler start before dagScheduler, so executor backend may register executor even before dagScheduler(or the eventProcessActor) has not initialized. in this situation it will throw NPE