Ticker Stop behaviour in Golang

Question

If I am ranging over a ticker channel and call stop() the channel is stopped but not closed.

In this Example:

package main

import (
    "time"
    "log"
)

func main() {
    ticker := time.NewTicker(1 * time.Second)
    go func(){
        for _ = range ticker.C {
            log.Println("tick")
        }
        log.Println("stopped")
    }()
    time.Sleep(3 * time.Second)
    log.Println("stopping ticker")
    ticker.Stop()
    time.Sleep(3 * time.Second)
}

Running produces:

2013/07/22 14:26:53 tick
2013/07/22 14:26:54 tick
2013/07/22 14:26:55 tick
2013/07/22 14:26:55 stopping ticker

So that goroutine never exits. Is there a better way to handle this case? Should I care that the goroutine never exited?

Answer 1

Used a second channel as Volker suggested. This is what I ended up running with:

package main

import (
    "log"
    "time"
)

// Run the function every tick
// Return false from the func to stop the ticker
func Every(duration time.Duration, work func(time.Time) bool) chan bool {
    ticker := time.NewTicker(duration)
    stop := make(chan bool, 1)

    go func() {
        defer log.Println("ticker stopped")
        for {
            select {
            case time := <-ticker.C:
                if !work(time) {
                    stop <- true
                }
            case <-stop:
                return
            }
        }
    }()

    return stop
}

func main() {
    stop := Every(1*time.Second, func(time.Time) bool {
        log.Println("tick")
        return true
    })

    time.Sleep(3 * time.Second)
    log.Println("stopping ticker")
    stop <- true
    time.Sleep(3 * time.Second)
}

Answer 2

you can do like this.

package main

import (
    "fmt"
    "time"
)

func startTicker(f func()) chan bool {
    done := make(chan bool, 1)
    go func() {
        ticker := time.NewTicker(time.Second * 1)
        defer ticker.Stop()
        for {
            select {
            case <-ticker.C:
                f()
            case <-done:
                fmt.Println("done")
                return
            }
        }
    }()
    return done
}

func main() {
    done := startTicker(func() {
        fmt.Println("tick...")
    })
    time.Sleep(5 * time.Second)
    close(done)
    time.Sleep(5 * time.Second)
}

Answer 3

If you need to save more space, use channels of empty structs (struct{}) which costs no memory. And as mentioned above, don't send something in it - just close, which actually sends zero value.