Subj : Re: A question about atomic_ptr
To   : comp.programming.threads
From : Peter Dimov
Date : Thu Apr 14 2005 05:53 pm

Joe Seigh wrote:
> The atomic swap is one part.  The other part is safely incrementing
> the reference count without "owning" it first.  There's the DWCAS
> solution, the PPC solution, and various GC based solutions using RCU,
> SMR, etc... And of course the 2CAS solution which only works on
> MC68020 and MC68030 processors.

You mean the race between

    atomic_ptr<T> p2( p1 );

and

    p1 = 0;

?

I think that you have a bug in your PPC implementation, but I may be missing 
something. In inc_ref, you reload the pointer and check for change, however, 
the pointer is a local function argument (int* refcnt) and will never 
change.

And you are right that Reinholz uses the same algorithm, except he passes an 
int** (the offset hack aside).

.