substack-concurrency-19.go

begin := make(chan interface{})
var wg sync.WaitGroup
for i:=0; i<5; i++ {
    wg.Add(1)
    go func(i int) {
        defer wg.Done()
        <- begin
        fmt.Printf("%v has begun\n", i)
    }()
}

fmt.Println("unblocking goroutines...")
close(begin)
wg.Wait()