using atomic builtins

[Peter Dimov]

Benjamin Kosnik wrote:
> Hey all!
>
> I've been reviewing some of the excellent work that Phillip is doing
> for summer of code.
>
> As part of that, I'm reviewing:
> http://mulliard.homelinux.org/~phillip/code/soc/patches/shared_ptr.patch

FWIW, the two

+#ifdef __GTHREADS
+ _GLIBCXX_READ_MEM_BARRIER;
+ _GLIBCXX_WRITE_MEM_BARRIER;
+#endif

blocks aren't necessary and can (should) be omitted, both because 
add_ref_lock requires no memory synchronization, and because (IIRC) the 
__sync_* functions already provide ordering.