The program is really racy, but the result is also really some
counter-intuitive.
The following program also print 10, which means evaluation of pointer
dereference
is some different to evaluation of other expressions in flow.
package main
import (
"fmt"
"time"
)
func main() {
var num = 10
var p = &num
c := make(chan int)
go func() {
c <- func()int{return *p}() // with this line we will get 11 from
channel c
//c <- num // with this line we will get 10 from channel c
}()
time.Sleep(time.Second)
num++
fmt.Println(<-c)
fmt.Println(p)
}
On Monday, September 4, 2017 at 10:35:32 PM UTC-4, Jesse McNelis wrote:
>
> On Tue, Sep 5, 2017 at 10:34 AM, Marlon Che <rob1...@gmail.com
> <javascript:>> wrote:
> > Hi everyone!
> > Please help me figure out the two different results of following code:
> >
> > package main
> >
> > import (
> > "fmt"
> > "time"
> > )
> >
> > func main() {
> > var num = 10
> > var p = &num
> >
> > c := make(chan int)
> >
> > go func() {
> > c <- *p // with this line we will get 11 from channel c
> > //c <- num // with this line we will get 10 from channel c
> > }()
> >
> > time.Sleep(2 * time.Second)
> > num++
> > fmt.Println(<-c)
> >
> > fmt.Println(p)
> > }
>
> You have a data race, what value you get from dereferencing p is
> undefined, it could be 10, it could be 11, it could wipe your
> harddrive or launch the missiles.
>
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