protected synchronized RemoteProcedureException getException() {
    if (subprocs != null) {
      for (Procedure<TEnvironment> proc : subprocs) {
        if (proc.hasException()) {
          return proc.getException();
        }
      }
    }
    return null;
  }
Called by the ProcedureExecutor to mark rollback execution
hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/RootProcedureState.java