In my application, I'm hooking various functions for creating COM objects (such as CoCreateInstanceEx) to get notified whenever some object is created. I'm keeping track of all created objects in a std::list and I'm iterating over that list to do various things (like checking which OLE objects have been activated).
The issue with this is that right now, whenever adding an IUnknown pointer to my list, I call IUnknown::AddRef on it to make sure that it doesn't get destroyed while I'm tracking it. That's not what I really want though; the lifetime of the object should be as long (or short) as it is without my tracing code, so I'd rather like to maintain a weak reference on the objects. Whenever the last reference to some tracked COM object is removed (and thus the object gets destroyed), I'd like to get notified so that I can update my bookkeeping (e.g. by setting the pointer in my list to NULL).*
What's the best way to do this? Right now, I'm patching the (first) VTable of all created objects so that the calls to IUnknown::Release via the first vtable get notified. However, this won't work for COM interfaces which inherit from multiple interfaces (and thus have multiple vtables), but I'm not sure whether this is really a problem: given the Rules for Implementing Q