anchor.diff:              case start_bench_child(Params, State) of
                   {ok, Id, NewState} ->
                       {reply, {ok, #{id => Id, status => <<"pending">>}}, NewState};
  -                {error, Reason} ->
  -                    {reply, {error, Reason}, State}
  +                {error, Reason, NewState} ->
  +                    {reply, {error, Reason}, NewState}
               end;
           {error, enoent} ->
               {reply, {error, not_found}, State};
  
positive.code:     case start_bench_child(Params, State) of
          {ok, Id, NewState} ->
              {reply, {ok, #{id => Id, status => <<"pending">>}}, NewState};
          {error, Reason} ->
              {reply, {error, Reason}, State}
      end;
  
  handle_call({start_bench, Params}, _From, #{status:= inactive} = State) ->
  
negative.code:             NewState = State#{next_id => Id + 1, monitors => maps:put(Mon, Id, Mons)},
              {ok, Id, check_max_bench_num(NewState)};
          {error, Reason} ->
              {error, Reason, State#{next_id => Id + 1}}
      end.
  
  check_max_bench_num(#{max_bench_num:= MaxNum, next_id:= NextId, data_dir:= Dir} = State) ->
  