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count / display the number of active goroutines

I have a queue and a function that does both dequeueing and enqueueing. I want to make sure that the right amount of goroutines operate on the queue, as long as there is something in the list.

This is the code I am using, but I was wondering if there is a way of printing the amount of currently active goroutines

Link to playground

var element int

func deen(queue chan int) {

    element := <-queue
    fmt.Println("element is ", element)
    if element%2 == 0 {
        fmt.Println("new element is ", element)
        queue <- (element*100 + 11)
        queue <- (element*100 + 33)
    }
}

func main() {
    queue := make(chan int, 10)
    queue <- 1
    queue <- 2
    queue <- 3
    queue <- 0 
    for len(queue) != 0 {
        for i := 0; i < 2; i++ {
            go deen(queue)
        }
    }
    fmt.Scanln()
    fmt.Println("list is has len", len(queue)) //this must be 0

}    
like image 794
meto Avatar asked Sep 26 '14 02:09

meto


1 Answers

There's runtime.NumGoroutine but you're approaching this wrong.

  1. Your loops will keep spawning goroutines.
  2. this will unnecessarily burn cpu cycles because of the for loop.

One approach is to use a sync.WaitGroup.

func deen(wg *sync.WaitGroup, queue chan int) {
    for element := range queue {
        fmt.Println("element is ", element)
        if element%2 == 0 {
            fmt.Println("new element is ", element)
            wg.Add(2)
            queue <- (element*100 + 11)
            queue <- (element*100 + 33)
        }
        wg.Done()
    }
}

func main() {
    var wg sync.WaitGroup
    queue := make(chan int, 10)
    queue <- 1
    queue <- 2
    queue <- 3
    queue <- 0
    for i := 0; i < 4; i++ {
        wg.Add(1)
        go deen(&wg, queue)
    }
    wg.Wait()
    close(queue)
    fmt.Println("list len", len(queue)) //this must be 0

}

playground

--- old buggy version with a race in it ---

func deen(wg *sync.WaitGroup, queue chan int) {
    for element := range queue {
        wg.Done()
        fmt.Println("element is ", element)
        if element%2 == 0 {
            fmt.Println("new element is ", element)
            wg.Add(2)
            queue <- (element*100 + 11)
            queue <- (element*100 + 33)
        }
    }
}

func main() {
    var wg sync.WaitGroup
    queue := make(chan int, 10)
    queue <- 1
    queue <- 2
    queue <- 3
    queue <- 0
    for i := 0; i < 4; i++ {
        wg.Add(1)
        go deen(&wg, queue)
    }
    wg.Wait()
    close(queue)
    fmt.Println("list is has len", len(queue)) //this must be 0
}

playground

like image 160
OneOfOne Avatar answered Nov 18 '22 22:11

OneOfOne