Delphi XE8 : Memory Leak with method datasnap server

Question

I'm currently designing a Datasnap rest server with Delphi. But I have serious memory leaks.

For example, my method station

procedure TV1.station(ID: integer);
begin


  GetInvocationMetadata().ResponseContent := Manager.xxxxxxAPI.GetObjectStation(ID);
  GetInvocationMetadata().CloseSession := true;     

end;

Which call this function :

function TSmmAPI.GetObjectStation( const ID: integer ) : string;
(...)
   jsonObject := TJSONObject.Create;   

          stationSelected := xxxxxManager.WorkShops.GetStation( CNCHandle );

          with StatesDB.QueryGetCurrentState( stationSelected.Handle ) do begin

            if RecordCount <> 0 then begin
              ConvertFileToPcom(stationSelected.Ini.FileName, Pcom);


              jsonObject.AddPair( TJSONPair.Create('ID', inttostr(ID)));
              jsonObject.AddPair( TJSONPair.Create('Name', FieldByName(sbStaStationField).AsString));
              jsonObject.AddPair( TJSONPair.Create('Workshop',  stationSelected.Shop.Name));
              jsonObject.AddPair( TJSONPair.Create('Group',  Pcom.Others.GroupName));                  
              jsonObject.AddPair( TJSONPair.Create('CurrentRef', FieldByName(sbStaRefNameField).AsString));
              jsonObject.AddPair( TJSONPair.Create('CurrentState', FieldByName(sbStaStateField).AsString));
              jsonObject.AddPair( TJSONPair.Create('Job', FieldByName(sbStaOPNameField).AsString));
              jsonObject.AddPair( TJSONPair.Create('Order',FieldByName(sbStaOFNameField).AsString));
               //(...), I have 12 addpair. 

              Disconnect;

            end;

            Destroy;
          end;// with StatesDB.QueryGetCurrentState


          result := jsonobject.toString;
          jsonObject.FreeInstance;
        end;

You can see, I use the resultContent instead of result from a function because I don't want result: in my json response.

So with the report from ReportMemoryLeaksOnShutdown, I see that all my jsonObject and each jsonpair are not destroy !!!

Result leak memory report, 5501 request from my client application

LifeCycle from the server class : Session

I use DSRESTWebDispatcher, set in Session Cycle and Timout at 60000.

Someone have an explanation? Did I forget to do something?

Dalija Prasnikar Dalija Prasnikar · Accepted Answer · 2015-10-26T12:23:12

You should call jsonObject.Free instead of jsonObject.FreeInstance

You should never call FreeInstance directly to release the object. It is part of internal allocation/deallocation mechanism. In Delphi destructors call FreeInstance automatically to deallocate object instance memory.

Proper ways to release object instances in Delphi are:

TObject.Free - calls object instance destructor if instance is not nil
TObject.DisposeOf - introduced with Delphi ARC mobile compilers and on dektop compilers it calls TObject.Free.
FreeAndNil(var Obj) - procedure that calls Free on passed object instance and nils that reference

Delphi XE8 : Memory Leak with method datasnap server

1 Answers