[fpc-pascal] Usage of TInterfacedObject. Automatic release?

Marc Weustink marc at dommelstein.net
Sun May 27 00:27:25 CEST 2007

Luiz Americo Pereira Camara wrote:
> Cesar Romero wrote:
>> Luiz Americo,
>>> Anyway, calling manually _Release avoid the leak and i will stay with 
>>> it for now (I hope did not break anything).
>> It can work for that case, but I think that is not a good ideia.
>> If you are using a TInterfacedObject descendant, it will call the 
>> _Release when out of context, so in that especific case seems to never 
>> go out of context, and then you _realease call works, but in other 
>> place it can go out of context before, and the you will have others AV.
>> - As Joao suggest, the best way is create a weak reference, where when 
>> 2 objects need to reference each other one should use Pointer to hold 
>> one reference
>> - Avoid circular reference
> The problem here is that i'm using a third party design. And the code 
> complexity allied with my inexperience with interfaces/COM makes the 
> chance of  breaking things big.
> Anyway i did not find, with my limitations, any circular references 
> between interfaces. Exists a circular reference but is between an 
> Interface (IVTDragManager) and a TVirtualTreeView(TCustomControl) 
> already used as a weak reference (TObject).
> The design is more or less the following:
> TBaseVirtualTree holds a reference to a IVTDragManager.
> TVTDragManager (IVTDragManager) holds a reference to TBaseVirtualTree 
> stored in a TObject field
> TVTDragManager also holds reference for IDataObject (TVTDataObject) and 
> IDropTargetHelper (returned by a win32 call)
> TVTDataObject holds a reference to TBaseVirtualTree as a TObject
> There are two circular references:
> TVTDragManager <-> TBaseVirtualTree
> TBaseVirtualTree <-> TVTDragManager > TVTDataObject > TBaseVirtualTree

Circular references of object is not the problem, you should look at 
circular references of interfaces.

However, I don't expect that this is the case for the virtualtree. THat 
you need a _release for fpc and not for delphi sounds like a bug in fpc. 
(only where)
Normally you never ever have to call _release yourself (unless you 
called _addref yourself)


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