On Friday, July 19, 2019 at 1:01:27 AM UTC+8, Ian Lance Taylor wrote:
>
> On Thu, Jul 18, 2019 at 8:35 AM T L <tapi...@gmail.com <javascript:>>
> wrote:
> >
> > For example:
> >
> > type Page struct {
> > views uint32
> > }
> >
> > func (page *Page) SetViews(n uint32) {
> > atomic.StoreUint32(&page.views, n)
> > }
> >
> > func (page *Page) Views() uint32 {
> > return atomic.LoadUint32(&page.views)
> > }
> >
> > Keith Randall and Ian Lance Taylor said that atomic.Load is a
> memory_order_acquire
> > and atomic.Store is memory_order_release, so there is no memory order
> guarantees
> > between the following two calls, I think:
> >
> > atomic.StoreUint32(&page.views, n)
> > atomic.LoadUint32(&page.views)
> >
> > In other words, the load result might not reflect the latest value of
> page.views.
>
> In these kinds of discussions it's hard to know what "latest value"
> means. But in general an atomic load will see any atomic store that
> preceded it in absolute time. The difference between load-acquire and
> sequentially-consistent-load is not with the atomic value itself; it's
> with all other memory accesses. The LoadUint32 will see the
> StoreUint32, but it may not see any other non-atomic memory stores
> done before the StoreUint32.
>
>
> > On the contrary, the memory order between the following two calls
> > is guaranteed to be as their order shown in code.
> >
> > atomic.LoadUint32(&page.views)
> > atomic.StoreUint32(&page.views, n)
> >
> > Is my understanding right?
>
> So, per above, not quite.
>
> And that said, see the more recent discussion on
> https://golang.org/issue/5045, in which Russ argues that we should use
> sequential consistency anyhow.
>
> Ian
>
Thanks, Ian. I get it now.
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