On 4 May 2017 at 13:49, Jonathan Wakely wrote: > On 4 May 2017 at 13:11, Toebs Douglass wrote: >> This being true if and only if the atomic load/store functions are used, >> right? and I suspect those functions are only issuing memory barriers? >> they do not use atomic operations themselves. If this is so, then all >> this is true, but there is within this absolutely no guarantee than any >> store on any core will ever *actually be seen* by any other core. If >> they *are* seen, *they will be in the correct order*, but there is no >> guarantee they *will* be seen. > > The C++ standard says: > > An implementation should ensure that the last value (in modification > order) assigned by an atomic or > synchronization operation will become visible to all other threads in > a finite period of time. > > "Should" in ISO-speak is strong encouragement, but not a guarantee. > However, it is expected that on all but the most esoteric hardware > platforms it will be true. > > I don't see equivalent wording in the C11 standard though. Ah, C11 says it in 7.17.3 Implementations should make atomic stores visible to atomic loads within a reasonable amount of time. C++ has that same wording, in addition to what I quoted above.
