Memory Leak in TDictionary - Problems with Workaround?

Question

Hi everybody,

I just considered using the new TDictionary type. But On QualityCentral I read about two memory leaks caused by TDictionary:

http://qc.codegear.com/wc/qcmain.aspx?d=67355

I just implemented the proposed workaround, basically subclassing TDictionary, overriding the destructor and manually freing the two objects that cause the leak:

destructor TMemCorrectedDictionary.Destroy;
begin
  Values.Free;
  Keys.Free;
  inherited;
end;

Problem is, since Values and Keys are read-only properties of TDictionary, I can't set them to nil. Well, just to be clear, everythings works fine now, but I wondered what would happen if CodeGear releases a patch for the leak and frees the two objects again in their own destructor. Wouldn't this cause an access violation?

Thanks in advance for reading (and hopefully answering).

Answer 1

You could call inherited first and check if the properties are still set:

destructor TMemCorrectedDictionary.Destroy;
begin
  inherited;
  Values.Free;
  Keys.Free;
end;

And by the way: Free doesn't care if the instance to be freed is nil, so this will work if (but only if) inherited Destroy sets the properties to nil.