apache/spark — pull request #3634 by zsxwing (2014-12-08 08:12:43+00:00)
Title: [SPARK-3154][STREAMING] Replace ConcurrentHashMap with mutable.HashMap and remove @volatile from 'stopped'

Since `sequenceNumberToProcessor` and `stopped` are both protected by the lock `sequenceNumberToProcessor`, `ConcurrentHashMap` and `volatile` is unnecessary. So this PR updated them accordingly.