Hi,
On Tuesday, April 24, 2012 22:51:34 James Turner wrote:
> Okay, I guess I was assuming I can use SGreferenced the same way I use
> release/retain in Cocoa, or addRef/decRef in COM/XPCOM. But it seems as if
> this is not the case, from looking at your commit - I can't use
> SGreferenced as a virtual base, and I have to make the delete call by hand.
>
> I guess this is to avoid virtual method overhead on SGreferenced?
Yes.
SGReferenced should exactly *not* contain any virtual table. This is supposed
to be the helper class for reference counting, but it should be as lightweight
as possible. Imagine we want at some time have a variable size mathematical
vector container that works with a copy on write semantics, I definitely want
to use SGReferenced there and have no vtable at all.
If you want something that you can just use a general base class for
heavyweight stuff, invent a class derived from SGReferenced or better
SGWeakReferenced that introduces this vtable stuff. And since we are looking
then for something more heavy, I would tend to use SGWeakReferenced as base
class for an SGObject
class SGObject : public SGWeakReferenced {
public:
virtual ~SGObject() {}
}
The weak referenced class provides the ability to have weak pointers to such a
WeakReferenced derived class. That are pointers that know about when the last
reference to the instance it points to is deleted and provides a
SGSharedPtr<T> SGWeakPtr<T>::lock() method that atomically and thread safe
returns either a valid shared pointer to the still alive object or a null
pointer since the objects reference count was already zero and the object is
at least being deleted or already dead.
If you want the destructor protected, I need to backport something more from
OpenRTI and stuff to simgear.
What about the mentioned problems? Better? Worse?
Mathias
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