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https://github.com/apache/spark/blob/ab8177da2defab1ecd8bc0cd5a21f07be5b8d2c5/core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala#L337
Simple omission on my part.
[Github] Pull Request #3612 (andrewor14)