proposal: time: Add TickerFunc

[sivchari]

Proposal Details

I propose TickerFunc to time package. This API is similar with time.AfterFunc.
Currently, if we execute some func regularly, we must write the code like following.

func main() {
	t := time.NewTicker(1 * time.Second)
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	go func() {
		for {
			select {
			case <-t.C:
				println("tick")
			case <-ctx.Done():
				return
			}
		}
	}()
        time.Sleep(N * time.Second)
        cancel()
        <-ctx.Done()
}

As you can see, this code is so complicated to what I want to do and if we forget the context or something to cancel, then this goroutine will be leaked.

TickerFunc(ctx context.Context, d Duration, f func()) *Ticker

The following code is example when I use time.TickerFunc.

func main() {
    ctx, cancel := context.WithCancel(context.Background())
    defer cancel()
    time.TickerFunc(ctx, 1*time.Second, func() {
        println("tick")
    })
    time.Sleep(N * time.Second)
    cancel()
    <-ctx.Done()
}

func TickerFunc(ctx context.Context, d time.Duration, f func()) *time.Ticker {
    t := time.NewTicker(d)
    go func() {
        for {
            select {
            case <-t.C:
                f()
            case <-ctx.Done():
                t.Stop()
                return
            }
        }
    }()
    return t
}

It's simpler than first one. In additional, since we must pass the context, we can prevent to leak goroutine.
This API is helpful to execute simple task which you want do repeatedly.

[gabyhelp]

Related Issues and Documentation

• proposal: time: add Ticker functions to affect the next tick #55129 (closed)

• proposal: time/tick.go: Ticker provide api to allow shared C among runtimeTimer objects #59920 (closed)

• proposal: time: allow Ticker to change duration #36544 (closed)

• [Package time > func Tick
  ¶

   	](https://go.dev/pkg/time/?m=old#Tick) <!-- score=0.85421 -->
  

• [Package time > type Ticker
  ¶

   	 \> func NewTicker
   			¶
   			
   			
   		](https://go.dev/pkg/time/?m=old#NewTicker) <!-- score=0.85348 -->
  

• proposal: Go 2: time: deprecate time.Tick(d Duration) #37144 (closed)

• proposal: time: NewTickerStartingAt and RuntimeStarted #43503

• proposal: time: add API to retrieve next trigger time for Timer and Ticker #66680 (closed)

• proposal: time: context-aware time Ticker and Timer #45571 (closed)

• time: add Ticker.Reset #33184 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

package time cannot import context, that would be a dependency cycle.

Do you have evidence of widespread use of this pattern in the ecosystem?

[ianlancetaylor]

This seems easy to write outside of the standard library. In fact, it looks like you already wrote it. https://go.dev/doc/faq#x_in_std

[rittneje]

time.AfterFunc returns a time.Timer so that you can stop it. If we did the same with time.TickerFunc, then I don't think there would be any need for the time package to reference the context package, avoiding the aforementioned import cycle.

t := time.TickerFunc(1*time.Second, func() {
    fmt.Println("tick")
})
context.AfterFunc(ctx, t.Stop)

[earthboundkid]

A related function that I have wanted which suffers from the time/context circularity is time.SleepContext, which would cancel a sleep if the context is closed. I think for now the best solution is to just put these in a personal utilities package, but I do wonder if something could be done in a Go 2.0 that combined context and time.