This trick is used in the standard library (see net.http.envOnce.reset), and for
testing purposes it's just about OK (though still dubious IMHO) but you should
never use it in production code, as you're writing atomic state with non-atomic
operations.
On 20 November 2017 at 00:24, Carl Mastrangelo
<carl.mastrang...@gmail.com> wrote:
> Hi gophers,
>
> I was playing around with a puzzle trying to break the sync package and
> found something cool. Can you think of a definition for f that causes
> once.Do to execute the argument more than once?
>
>
> package main
>
> import (
> "sync"
> )
>
> func main() {
> var once sync.Once
> var f = // ...
>
> once.Do(f)
> }
>
>
> HIGHLIGHT BELOW FOR ANSWER
>
>
> package main
>
> import (
> "fmt"
> "sync"
> )
>
> func main() {
> var once sync.Once
> var f func()
> times := 9
> f = func() {
> if times == 0 {
> return
> }
> times--
> fmt.Println("Called")
> oldonce := once
> *&once = sync.Once{}
> once.Do(f)
> once = oldonce
>
> }
> once.Do(f)
> }
>
> HIGHLIGHT ABOVE FOR ANSWER
>
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