Resetting a ticker in Go

Raft is the distributed consensus algorithm that I’m using for the database I’m building at the Recurse Center. The algorithm has two timeouts — a heartbeat timeout and an election timeout. When a server receives a heartbeat from the leader, it resets its election timeout. If it doesn’t receive a heartbeat before its election timeout runs out, it tries to elect itself as leader!

As a first step towards this, I need to write code that resets a timeout (say 2 seconds) every time another timeout (say 5 seconds) expires. I would expect to see output that looked like:

Elapsed: 0
Elapsed: 2 Ticker A
Elapsed: 4 Ticker A
Elapsed: 5 Ticker B - Going to reset Ticker A!
Elapsed: 7 Ticker A
Elapsed: 9 Ticker A

Elapsed: 0 
Elapsed: 2 Ticker A
Elapsed: 4 Ticker A
Elapsed: 5 Ticker B
Elapsed: 6 Ticker A
Elapsed: 8 Ticker A

Here’s how I wrote this in Go, using ticking channels. I set up a goroutine that listens on two channels, tickerA and tickerB. Every time tickerB goes off, it resets tickerA.

type server struct {
    doneChan chan bool
    tickerA  ticker
    tickerB  ticker
}

func (s *server) listener() {
    start := time.Now()
    for {
        select {
        case <-s.tickerA.ticker.C:
            elapsed := time.Since(start)
            fmt.Println("Elapsed: ", elapsed, " Ticker A")
        case <-s.tickerB.ticker.C:
            s.tickerA.resetTicker()
            elapsed := time.Since(start)
            fmt.Println("Elapsed: ", elapsed, " Ticker B - Going to reset ticker A")
        }
    }
    s.doneChan <- true
}

func main() {
    doneChan := make(chan bool)
    tickerA := createTicker(2 * time.Second)
    tickerB := createTicker(5 * time.Second)
    s := &server{doneChan, *tickerA, *tickerB}
    go s.listener()
    <-doneChan
}

type ticker struct {
    period time.Duration
    ticker time.Ticker
}

func createTicker(period time.Duration) *ticker {
    return &ticker{period, *time.NewTicker(period)}
}

func (t *ticker) resetTicker() {
    t.ticker = *time.NewTicker(t.period)
}

$ go run tick.go

Elapsed:  2.00074535s  Ticker A

Elapsed:  4.002086857s  Ticker A

Elapsed:  5.004973744s  Ticker B - Going to reset ticker A

Elapsed:  7.008515813s  Ticker A

Elapsed:  9.009572001s  Ticker A

Arpith Siromoney 💬

Resetting a ticker in Go