Srivathsan Madhavan <[email protected]> wrote:
> Hi all,
>
> I still consider myself a newbie to Golang hence my question here could be
> due to my fundamental misunderstanding of this language
>
> I have the following code:
>
> func main() {
>
> for i := 0; i < 5; i++ {
>
> go func() {
>
> log.Println("i=", i)
>
> }()
>
> }
>
>
> fmt.Print("Press <Enter> to quit...")
>
> var input string
>
> fmt.Scanln(&input)
>
> }
>
>
> The output I expect is 0, 1, 2, 3, and 4 in any jumbled order. But what I
> got was 5, 5, 5, 5 and 5! Why is that so?
>
I'm learning golang too so please correct any errors here.
It looks like you created a closure where i is lexically scoped to
each of your gofunc() instances. Since they're all accessing the same
i variable, you're seeing the race between incrementing i and spooling
up / starting each goroutine -- that is, the value of i reaches 5
before all of the goroutines get to print it. You can verify this by
printing the address of i by changing your log.Println() call to
something like:
log.Printf("i = %d, &i = %p", i, &i)
The addresses should be the same.
If you want each goroutine to have a copy of I, you should declare and
run gofunc() like below:
gofunc(c int) {
log.Println("c=",c)
}(i)
Which passes a copy of i to each routine. That should give you what
you're looking for -- that is if you're not expecting i to be printed
in order. :)
-ayan
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