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Weak reference count modifications do not need to be locked...
That's good to know.
You don't need to use DWCAS either...
Don't I need to do that for assignment and compare_and_set for the actual shared_ptr<>, since it's two words? (pointer to object and pointer to refcount.)
Well, if you use the current shared_ptr<> implementation, then the answer is yes. I was referring to the fact that you can create shared_ptr<> out of a completely different implementation that is "mostly" lock-free and 100% compatible with plain-ol' CAS. I created and prototyped an experimental example of such an algorithm. IMO, it proves that it is possible for a single-word atomic refcounting implementation to exist without the support from any sort of PDR algorithm.
This is good feedback. Thank you for the help.
No problem. :^)