private void rolllog() throws ForeignException {
    monitor.rethrowException();

    taskManager.submitTask(new RSRollLogTask());
    monitor.rethrowException();

    // wait for everything to complete.
    taskManager.waitForOutstandingTasks();
    monitor.rethrowException();
  }
Callable task. TODO. We don't need a thread pool to execute roll log. This can be simplified
with no use of sub-procedure pool.
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/regionserver/LogRollBackupSubprocedure.java