On Friday, 29 December 2017 16:55:37 UTC+11, Caleb Spare wrote: > > > My argument is all that 'happens-before' is a comparison of o.done == > > 0 happens before the address of o.done is passed to > > atomic.StoreUint32. The rest is just luck. > > This expression: > > atomic.StoreUint32(&o.done, 1) > > does not just take the address of o.done. It also executes the > StoreUint32 function, which is defined by the sync/atomic > documentation to behave like '*o.done = 1'; i.e., it alters the value > of o.done.
Respectfully I disagree, it store the value 1 at the memory address &o.done. It has no defined effect on other occurrences of o.done in this, or other goroutines if they have already loaded o.done. I agree that i'm still talking about registers and inlining; but if there were no registers, inlining, caches, or other things which are not specified by the language, then there would be no data races. So here we are. > When I say that there's a total ordering among the reads > and writes within the mutex, this is the write that I'm referring to. > > > I agree it should print 2, but my reading of the memory model and > > https://github.com/golang/go/issues/5045 doesn't give me any concrete > > guarantee that it must. This is why i'm not sure about the > > interactions between atomic and non atomic loads. > > Here, too, I think we need to turn to the sync/atomic documentation, > which says what the effect of StoreUint32 is. The precise nature of > concurrent atomic operations can be left to #5045, but here we are > concerned with something simpler: after StoreUint32 returns > ("after" in a happens-before sense), are we guaranteed to read the > stored value? The answer must be yes. (If the answer were no, then > StoreUint32(p, val) would be in some sense *less atomic* than the > statement *p = val.) > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
