apache/spark — pull request #3781 by sarutak (2014-12-24 04:36:08+00:00)
Title: [SPARK-4949] [SPARK-4949] shutdownCallback in SparkDeploySchedulerBackend should be enclosed by synchronized block.

A variable `shutdownCallback` in SparkDeploySchedulerBackend can be accessed from multiple threads so it should be enclosed by synchronized block.