Delphi 2009 interface

Question

I have this code and at the end of it, FastMM shows that there were memory leaks with all the objects of TSinc:

unit sinc_int;
interface
uses
 Classes,
 log_listener_list_int,
 tick_listener_list_int;
type
 ISinc = interface;
 ISincList = interface;
 ISinc = interface ['{53814230-6308-4259-99FF-6054F2C91F9C}']
 function Execute: Boolean;
 function SincList: ISincList;
 function Log: string;
 procedure AddLog(const Texto: string);
 function LogListenerList: ILogListenerList;
 function TickListenerList: ITickListenerList;
 function SincIntervaloMili: Integer;
 function EstaSincronizando: Boolean;
 procedure Start;
 procedure Stop;
 end;
 ISincList = interface ['{F3355798-4584-4DCE-8EBA-3692B14FA132}']
 function Add(const Item: ISinc): Integer;
 function Count: Integer;
 function Get(const Index: Integer): ISinc;
 procedure Put(const Index: Integer; Item: ISinc);
 procedure Remove(const Item: ISinc);
 procedure Clear;
 procedure Start;
 procedure Stop;
 end;
implementation
end.
unit sinc_class;
interface
uses
 sinc_int, log_listener_list_int, tick_listener_list_int, sinc_thread_class;
type
 TSinc = class (TInterfacedObject, ISinc)
 protected
 FLog: string;
 FSincList: ISincList;
 FLogListenerList: ILogListenerList;
 FTickListenerList: ITickListenerList;
 FSincIntervaloMili: Integer;
 FEstaSincronizando: Boolean;
 FThread: TSincThread;
 public
 constructor Create; virtual;
 destructor Destroy; override;
 function Execute: Boolean; virtual; abstract;
 function SincList: ISincList;
 function Log: string; virtual;
 procedure AddLog(const Texto: string);
 function LogListenerList: ILogListenerList;
 function TickListenerList: ITickListenerList;
 function SincIntervaloMili: Integer;
 function EstaSincronizando: Boolean;
 procedure Start;
 procedure Stop;
 end;
implementation
uses
 sinc_list_class,
 log_listener_list_class,
 tick_listener_list_class;
{ TSinc }
procedure TSinc.AddLog(const Texto: string);
begin
 FLogListenerList.AddLog(Texto);
 FLog:=FLog+Texto;
end;
constructor TSinc.Create;
begin
 FSincList:=TSincList.Create;
 FLogListenerList:=TLogListenerList.Create;
 FTickListenerList:=TTickListenerList.Create;
 FEstaSincronizando:=False;
 FThread:=TSincThread.Create(Self);
end;
destructor TSinc.Destroy;
begin
 FSincList.Clear;
 FSincList:=nil;
 FLogListenerList.Clear;
 FLogListenerList:=nil;
 FTickListenerList.Clear;
 FTickListenerList:=nil;
 FThread.Free;
 inherited;
end;
function TSinc.EstaSincronizando: Boolean;
begin
 Result:=FEstaSincronizando;
end;
function TSinc.Log: string;
begin
 Result:=FLog;
end;
function TSinc.LogListenerList: ILogListenerList;
begin
 Result:=FLogListenerList;
end;
function TSinc.SincIntervaloMili: Integer;
begin
 Result:=FSincIntervaloMili;
end;
function TSinc.SincList: ISincList;
begin
 Result:=FSincList;
end;
procedure TSinc.Start;
begin
 FEstaSincronizando:=True;
 FSincList.Start;
 FThread.Resume;
end;
procedure TSinc.Stop;
begin
 FThread.Suspend;
 FSincList.Stop;
 FEstaSincronizando:=False;
end;
function TSinc.TickListenerList: ITickListenerList;
begin
 Result:=FTickListenerList;
end;
end.

And when I do this:

procedure TForm2.btnSinc1Click(Sender: TObject);
begin
 SincTest:=TSincTest.New;
 SincTest:=nil;
end;

It shows that there were memory leaks with the TSincTest class, its lists and even the thread.

• Phrancis: Welcome to Code Review. Please see Checklist for how to write a good Code Review question. Please also clarify if your program runs as expected, minus the memory leaks, or if the memory leaks cause fatal errors/crash of your program.
• Luiz Carlos M. Jr.: @Phrancis Thank you. I'll correct my question with the checklist and the points you made.
• Ken Bourassa: My guess, you declared SincTest : TSincTest instead of SincTest : ISinc, but you don't supply enough information to know for sure.

Answer 1

I suggest to check around TSync as it inherits from TInterfacedObject, which is reference counted, a typical source of memory leak.

Answer 2

Unless Delphi syntax has changed since I was writing it, this code will not free the memory allocated to these object, just dereference the pointer.

 FSincList.Clear;
 FSincList:=nil;
 FLogListenerList.Clear;
 FLogListenerList:=nil;
 FTickListenerList.Clear;
 FTickListenerList:=nil;

instead of

 FSincList.Clear;
 FSincList:=nil; 

just call

 FSincList.free;

This will free the memory. You can set it to nil also if you wish.