Goroutine select loop with Ticker causes CPU to 100%

Question

I have this loop that what it does is trying to repeatedly poll to another server. I used ticker to achieve this however the program repeatedly shows 100% CPU usage.

This ticker runs inside a goroutine. and the HTTP server runs inside another goroutine.

func() Monitor() {

  abort := make(chan bool)

  log.Info("Monitor started.")

  // start the monitor goroutine
  go func() {
      defer log.Info("Stopped monitor")
        
      ticker := time.NewTicker(time.Duration(35.0) * time.Second)
      defer ticker.Stop()
        
      log.Info("Monitor started! \n")
      for {
        select {
        case t := <-ticker.C:
            log.Infof("Subscribe to service at time %v\n", t)
            if err := selfConn.SubscribeToService(); err != nil {
                log.Errorf("Failed to subscribe to primary connector: %v", err)
            } 
        case <-abort:
            log.Info("Finished routine!")
            return
        default:
            continue
        }
        }
    }() 
  
    go func() {
        time.Sleep(10 * time.Minute)
        abort <- true
    }()
}

However when monitor loops start, and everytime the signal to the ticker channel is sent, the CPU shows 100% constantly.

What have I missed in using ticker in the goroutine so that it won't consume 100% CPU?

Answer 1

You have a select with a default branch inside your loop. If none of the other case s are ready to proceed, the default branch is executed immediately, so your next iteration begins immediately without wait. This is a busy loop.

Also, there is no need for another goroutine to terminate, you could use a timer for that in the same goroutine.

For example:

func monitor() {
    log.Info("Monitor started.")

    ticker := time.NewTicker(35 * time.Second)
    defer ticker.Stop()

    timeoutCh := time.After(10 * time.Minute)
    for {
        select {
        case t := <-ticker.C:
            log.Infof("Subscribe to service at time %v\n", t)
            if err := selfConn.SubscribeToService(); err != nil {
                log.Errorf("Failed to subscribe to primary connector: %v", err)
            }
        case <-timeoutCh:
            log.Info("Finished routine!")
            return
        }
    }
}