Surely single goroutine scenarios are trivial? Anything else would be a
compiler bug. In multiple goroutine scenarios a lock must be held or some
of the atomic functions are needed. Any other use that "works" are by
accident say on x86 or some other stricter arch. I am no expert in this but
surely hope this is true because much of my code depends on it...
On Fri, Dec 29, 2017, 09:57 Caleb Spare <cesp...@gmail.com> wrote:
> > I believe that program will always print 2, however when you bring
> multiple Goroutines into the mix, I’m less sure.
>
> I'm using examples without goroutines because the crux of our
> discussion, as I understand it, is whether a plain read ('if o.done ==
> 0') will read the result of an atomic write
> ('atomic.StoreUint32(&o.done, 1)') given that there is a
> happens-before relationship between them.
>
> The simplest kind of happens-before relationship is that between
> sequential lines of straight-line code in a single goroutine. If you
> agree that the mutexes imply a happens-before relationship between the
> atomic write and the plain read, then we can simplify the discussion
> by only considering sequential code in a single goroutine.
>
> Regarding the sequential, single-goroutine example code: for my first
> example with atomic.StoreUint32
> (https://play.golang.org/p/fdf8VeJ98Jv), you wrote
>
> > 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.
>
> but for the second example with a non-atomic store function
> (https://play.golang.org/p/gk3c6X_JdmQ), you wrote
>
> > I believe that program will always print 2
>
> What's the distinction you see between them?
>
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