[fpc-devel] Proof of Concept ARC implementation

[Hans-Peter Diettrich]

Sven Barth schrieb:
> Am 25.10.2014 03:17 schrieb "Hans-Peter Diettrich" <DrDiettrich1 at aol.com 
> <mailto:DrDiettrich1 at aol.com>>:
>  >> - a class instance is destroyed once the reference count reaches 
> zero (and Free does not work for them)
>  >
>  >
>  > Shouldn't Free be usable as a finalizer, clearing all references to 
> other objects within this instance?
> 
> One could do that (for now I've chosen the simple way). One would 
> however need to check how this would be implemented best (e.g. it should 
> be marked somehow so that the destructor later on does not try to work 
> with already finalized fields; also all fields (Strings, arrays, 
> interfaces, records, etc.) should be finalized so that it is 
> consistent).

A finalizer must clear all managed fields, otherwise memory management 
were corrupted. Doing so may destroy other managed objects, so that 
possible consequences must be considered. I wonder whether the sequence 
of clearing fields may cause trouble?

> Also it needs to be observed how other reference holders 
> might react to that "zombie" instance.

Right, this should be considered by the developer.

> A further problem might be legacy 
> code which gets passed a reference counted instance (on which ARCIncRef 
> was called to keep it alive) and which then calls Free. Might not be the 
> intended result by neither code... This might be the reason of 
> Embarcadero to implement Free as a no-op and add a new DisposeOf which 
> does what you suggested.

Then Delphi compatibility has to be maintained. Is DisposeOf fully 
automatic, or can it be overridden or otherwise influenced (field 
sequence...)?

DoDi