function ReadData(var Data:TData; PointData:THI_Event; Def:PData):TData;
begin
   if Assigned(PointData.Event) then
     begin
       Result.Data_type := data_null;
       //Result.Next := nil;
       _hi_OnEvent(PointData,Result);
     end
   else if(Def = nil)or( Def.data_type = data_null ) then
    begin
     Result := Data;
      {$ifdef MT_ENABLED}
      if Data.ldata <> nil then
        Data := Data.ldata^
      else
      {$endif}
     Data.data_type := data_null;
    end
   else Result := Def^;
end;

    .....
    begin
     Result := Data;
     {$ifdef MT_ENABLED}Result.ldata := nil;
     if Data.ldata = nil then Data.data_type := data_null;
     if Data.data_type <> data_null then Data := Data.ldata^;
     {$else}Data.data_type := data_null;{$endif}
    end
   else Result := Def^;
end;