In my write goroutine I don't modify the map key (data structure) but set
the variable point to another map address ,this is a pointer assignment
and is atomic
在 2016年11月4日星期五 UTC+8下午1:22:20，Ian Lance Taylor写道：
>
> On Thu, Nov 3, 2016 at 10:19 PM, 刘桂祥 <liuguix...@gmail.com <javascript:>>
> wrote:
> > can you explain why whis ?
>
> A map is basically a pointer to a complex data structure. Setting a
> value in a map changes that data structure. If one goroutine is
> reading from the data structure while a different goroutine is writing
> to the data structure, the results are completely unpredictable. In
> the worst case they could even cause the program to crash.
>
> Ian
>
>
> > 在 2016年11月4日星期五 UTC+8下午1:16:39，Ian Lance Taylor写道：
> >>
> >> On Thu, Nov 3, 2016 at 8:37 PM, 刘桂祥 <liuguix...@gmail.com> wrote:
> >> > // example.go
> >> >
> >> > package main
> >> >
> >> > var gMap = make(map[int]int)
> >> >
> >> > func w() {
> >> > temp := make(map[int]int)
> >> > temp[1] = 100
> >> > temp[2] = 200
> >> > gMap = temp // Does the compiler or cpu will reorder
> temp[1]=100,
> >> > temp[2]=200, gMap=temp ??
> >> > }
> >> >
> >> > func r() {
> >> > local := gMap
> >> > println(local[1], local[2])
> >> > }
> >> >
> >> > func main() {
> >> >
> >> > go w()
> >> > go r()
> >> >
> >> > // ...
> >> > }
> >> >
> >> > I have one goroutine to read the map and one goroutine to rewrite the
> >> > global
> >> > map variable does this safe ??
> >>
> >> No. Use a lock.
> >>
> >> Ian
> >
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