public static class DagManager.DagManagerThread extends Object implements Runnable
DagManager.DagManagerThread performs 2 actions when scheduled:
Dags from the Dag queue. All the JobExecutionPlans which
are part of the dequed Dag will be managed this thread. public void run()
DagManager.DagManagerThread. Deque the next item from the queue and poll job statuses of currently
running jobs.
Because this thread runs in a regular interval, we should avoid doing repetitive work inside it.