@Override
    public void acquireBarrier() throws ForeignException {
      // do nothing, executing in inside barrier step.
    }
Callable task. TODO. We don't need a thread pool to execute roll log. This can be simplified
with no use of subprocedurepool.
hbase-server/src/test/java/org/apache/hadoop/hbase/procedure/SimpleRSProcedureManager.java