如何实现弹出->做某事->使用goroutines推送队列

Question

I have a queue and I would like to perform the following operations:

• pop the first element

• If the element is even, push element +1

This should go on until the queue is empty; furthermore I want to use multiple goroutines at the same time.

I am able to do for a single goroutine, but as soon as I add a while everything goes wrong, since it appears that too many goroutines are created. Even putting a else {return} will not solve the problem. Side question: why not? I get the errors:

syntax error: unexpected semicolon or newline before else
syntax error: unexpected }

Link to Playground

var list = []int{0, 1, 2, 3}

var mutex = &sync.Mutex{}

func pop(out chan int) {
    mutex.Lock()
    element := list[0]
    fmt.Println("element is ", element)
    list = list[1:]
    mutex.Unlock()
    out <- element
}

func push(in chan int) {
    for element := range in {
        if element%2 == 0 {
            mutex.Lock()
            list = append(list, element+1)
            fmt.Println("New list is ", list)
            mutex.Unlock()
        }
    }
}

func main() {
    out := make(chan int)
    fmt.Println("MAIN")

//  for len(list) != 0 {
    go pop(out)
    go push(out)
//}
    time.Sleep(2)
}

Answer 1

Multiple problems with your code.

• else is always on the same line as if's closing brace. Please read the Spec on this.

• time.Sleep takes time.Duration as its argument, which is in nanoseconds. If you want to sleep for 2 seconds, use time.Sleep(2*time.Second).

• for range in push is not needed.

• Your for for just spawns millions of goroutines over and over. Goroutintes are lightweight, but not free. Add some kind of synchronisation mechanism to control how many goroutines you are running.

Here is a slightly better version. It works, even though using time.Sleep as a synchronisation mechanism is something you should never do.