什么时候执行下一个goroutine？

I am looking at the example from https://blog.golang.org/pipelines:

func main() {
    in := gen(2, 3)

    // Distribute the sq work across two goroutines that both read from in.
    c1 := sq(in)

    // When does this line below execute and what is in `in`?
    c2 := sq(in)

    // Consume the merged output from c1 and c2.
    for n := range merge(c1, c2) {
        fmt.Println(n) // 4 then 9, or 9 then 4
    }
}

When does c2 := sq(in) run? As what I understand, it executes not when previous line finishes, but instantly as that is a goroutine.

Will c2 receive the next incoming message that is after coming after the message that is received by c1?

Your code does not use goroutines, in order to use go routines you should do something like this:

q := make(chan type) 
go sq(in, q)
go sq(in, q)

for elem := range q {
    fmt.Println(elem)
}

and sq must return the value through a channel

func sq(in type, q chan type) {
     ...
     q <- valueFromIn
     ...
}

Also you can use WaitGroup to wait for goroutines to finish.