@Override
    protected LockState acquireLock(final MasterProcedureEnv env) {
      if (env.getProcedureScheduler().waitServerExclusiveLock(this, getServerName())) {
        return LockState.LOCK_EVENT_WAIT;
      }
      return LockState.LOCK_ACQUIRED;
    }
Confirm that we will do backoff when retrying on closing a region, to avoid consuming all the
CPUs.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestCloseRegionWhileRSCrash.java