golang memory model?

[xie cui]

here is the code:

package main

import "fmt"

func main() {

counter := 0

ch := make(chan struct{}, 1)

closeCh := make(chan struct{})

go func() {

counter++     //(1)

ch <- struct{}{}

}()

go func() {

_ = <-ch

fmt.Println(counter) //(2)

close(closeCh)

}()

_ =<-closeCh

}

is (1) happens before (2)? why?

[Axel Wagner]

Yes.

1. `counter++` happens-before `ch <- struct{}{}`, because in a single goroutine, happens-before is equivalent with lexical statement order

2. `ch <- struct{}{}` happens-before `<-ch` completes, because "A send on a channel happens before the corresponding receive from that channel completes".

3. `<-ch` completion happens-before `fmt.Println(counter)`, again because in a single goroutine, happens-before is equivalent with lexical statement order

Therefore, `counter++` happens-before `fmt.Println(counter)`.

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[Shulhan]

I believe the answer is not g. https://golang.org/ref/mem#tmp_7