On Sat, Jul 13, 2013 at 12:24 AM, Richard Henderson <r...@twiddle.net> wrote: > On 07/11/2013 11:32 PM, Liu Ping Fan wrote: >> Refcnt's atomic inc/dec ops are frequent and its idiom need no seq_cst >> order. So to get better performance, it worth to adopt _relaxed >> other than _seq_cst memory model on them. > > You'd need to update the documentation then. As it stands, what you've > written > looks like a bug. > Ok, will update atomic.txt
>> +#ifndef _GLIBCXX_ATOMIC_BUILTINS > > This will never be defined. It's private to the libstdc++ implementation. > See > how we've defined things using __atomic elsewhere in the file, looking at one > of the __ATOMIC defines. > Oh, I misunderstood the description of _GLIBCXX_ATOMIC_BUILTINS. Got it, thanks. > And in either case, it's better form to use positive tests than negative ones. > I.e. #ifdef rather than #ifndef > Will fix. >> #define atomic_fetch_inc(ptr) __sync_fetch_and_add(ptr, 1) >> #define atomic_fetch_dec(ptr) __sync_fetch_and_add(ptr, -1) > > I'd prefer atomic_fetch_inc_relaxed, as that's more self-documenting. > But if _relaxed not supported, it will fall back on _seq_cst, then atomic_fetch_inc_relaxed will be wrong named? Thanks and regards, Pingfan > But I'll re-iterate the necessity of documentation in this area. > > > r~