sorry could you provide a complete example ?
I try this but not find question
package main
import "time"
type T struct{ x int }
var global *T
func f() {
p := new(T)
p.x = 1
global = p // "publish" the new T (racy!)
}
func g() {
p := global
if p != nil {
// println(p.x) // may print "0" due to data race
if p.x == 0 {
panic("ca")
}
}
}
func main() {
for i := 0; i < 10000; i++ {
go func() {
for j := 0; j < 1000; j++ {
f()
}
}()
go func() {
for j := 0; j < 1000; j++ {
g()
}
}()
}
time.Sleep(100 * time.Second)
}
在 2016年9月13日星期二 UTC+8上午5:28:37，adon...@google.com写道：
>
> On Monday, 12 September 2016 12:04:30 UTC-4, sqweek E. wrote:
>>
>> Yes, through plain assignment. What problems arise from that?
>>
>
> Here's the general form of the problem. In the code below, one goroutine
> (f) creates a variable, initializes it (x=1), then shares its address with
> another goroutine (in this case by assigning to a global variable, but
> that's a detail). Another goroutine (g) reads the pointer out of the
> global variable and inspects the variable to which it points.
>
> type T struct { x int }
>
> var global *T
>
> func f() {
> p := new(T)
> p.x = 1
> global = p // "publish" the new T (racy!)
> }
>
> func g() {
> p = global
> if p != nil {
> println(p.x) // may print "0" due to data race
> }
> }
>
> go f()
> go g()
>
> One might naively think that the print statement always prints 1, but in
> fact it can print 0. The reason is that the compiler or CPU is free to
> reorder the assignments p.x=1 and global=p, since f can't tell. But
> reordering means other goroutines might observe a non-nil pointer in global
> before the thing it points to has been fully initialized.
>
> To safely "publish" a variable initialized by one goroutine so that other
> goroutines see it properly initialized, you need "barrier semantics", that
> is, you need to tell the compiler and CPU not to reorder those assignments.
> That's what atomic.Value does.
>
> But you shouldn't reach for atomic.Value without data. In most programs,
> a mutex is simpler to reason about and plenty fast enough.
>
>
--
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.
