On Sun, Oct 30, 2022 at 10:16 AM Konstantin Khomoutov <kos...@bswap.ru> wrote:
>
> | initially, y==0.
> |
> | goroutine 1:
> | x = 42
> | x = 99
> | atomic.Store(&y, 1)
> | x = 100
> |
> | goroutine 2:
> | if atomic.Load(&y) == 1 {
> | println(x)
> | }
>
> then would println have been guaranteed to still print 99 and not 100?
No. (But it definitely wouldn't print 42.)
> In other words, do I understand correctly that an atomic write-like operation
> guarantees that all stores made by a goroutine before that operation must be
> visible, but stores made afterwards may be visible or not visible?
Yes.
> Or, to put it differently, if the read from y in goroutine 2 sees a 1,
> there's no way println(x) prints 42, but it may print 99 or 100.
Yes.
> ..and also if x is not naturally aligned (I think it's impossible in Go) or
> not "hardware atomic" - like a 64-bit integer on a 32-bit platform, -
> println(x) could produce some weird value as a result of the torn write/torn
> read which may happen when one core updates the x while another one reads it,
> right?
Well, this case is not supported in general, but I think the answer is yes.
Ian
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