substack-concurrency-8.go

c := sync.NewCond(&sync.Mutex{})
queue := male([]interface{}, 0, 10)

removeFromQueue := func(delay time.Duration) {
    time.Sleep(delay)
    c.L.Lock()
    queue = queue[1:]
    c.L.Unlock()
    c.Signal() // <- let a goroutine waiting for a condition to know that smth happened
}

for i:=0; i<10; i++ {
    c.L.Lock()
    for len(queue) == 2 {
        c.Wait()
    }
    queue = append(queue, struct{}{})
    go removeFromQueue(1*time.Second)
    c.L.Unlock()
}