On 4 May 2017 at 14:15, Toebs Douglass wrote: > On 04/05/17 15:05, Jonathan Wakely wrote: >> On 4 May 2017 at 13:58, Toebs Douglass wrote: >>> On 04/05/17 14:44, Jonathan Wakely wrote: >>>> Although there are also relaxed atomic operations (on atomic types) >>>> which are not synchronization operations. Not all atomic operations >>>> provide sequential consistency. >>> >>> If you had multiple cores issuing CAS with consume on a single variable, >>> you'd get total order, I think? and you wouldn't with relaxed because >>> with relaxed you wouldn't get a compiler barrier. >> >> Forget about consume. It's underspecified, poorly understood and >> poorly implemented. > > GCC says it promotes consume to acquire. However, I *think* I > understand consume (I almost certainly don't, of course :-) and it is > something I do use in my code - I hope GCC gets it right one day. I may > be completely wrong, but I might go out on a limb and say it's the > difference between emitting no barriers (relaxed), a compiler barrier > (consume), or a compiler and memory barrier (acquire). See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0371r1.html
