Subj : Re: A question about atomic_ptr
To   : comp.programming.threads
From : Peter Dimov
Date : Thu Apr 14 2005 03:01 pm

Joe Seigh wrote:
> I was going to say it is probably the only working atomic ptr out
> there. If you google for "Lock-free Reference Counting" you'll find a
> paper on on an implementation that requires an instruction no longer in
> existence. However google dragged up an article in the Dec 2004 CUJ
> titled "Atomic Reference Counting Pointers" by William K. Reinholtz
> which going by the code examples appears to be the same as the PPC
> version of atomic_ptr. I don't have access to the article itself so I 
> don't know where he got
> the algorithm.  Anyone know?

Since it's in CUJ, you should probably ask in clc++m. William K. (Kirk) 
Reinholtz has several RT-related papers, so if he doesn't give you credit in 
the article, he probably invented it.

By looking at

ftp://ftp.cuj.com/pub/2004/cujdec2004.zip

I'd say that it doesn't have much in common with your atomic_ptr. Macros vs 
templates and the definition of CAS aside, atomic_ptr is non-intrusive, 
Reinholtz's 'rcp' is intrusive; it relies on a cntr_ member in the pointee 
to keep the count. It's like boost::intrusive_ptr with an atomic exchange in 
the 'swap' member, except with most of the code inlined and some 
over-atomicity in the constructors and the destructor. No match for your 
atomic_ptr, IMO.

.