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

Luiz Americo Pereira Camara pascalive at bol.com.br
Mon May 28 00:28:51 CEST 2007

Marc Weustink wrote:
> 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.
As i explained i did not found interface circular references. (Although 
does not mean it does not exists ;-))
> 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)
This was my first idea. And now gains force again. The problem is that 
the bug can not be isolated easily.

Another option is that there's a mem leak in delphi also. Does some one 
know how to trace a mem leak in delphi?


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