关于 mainLoop 方法的一些疑问

[moonheart]

你好，我在看源码的时候对 mainLoop 方法的实现有一些疑惑，还望解答。

按照我的理解，mainLoop 方法的作用是从 pushChannel 接收 consul 服务的变化事件，对事件进行去抖动（debounce），然后触发 pushConsulService2APIServer 方法。

第一个是在这段代码对 pushChannel 的处理中

consul2istio/pkg/controller.go

Lines 109 to 117 in 4e4ed84

	case e := <-s.pushChannel:
	log.Debugf("Receive event from push chanel : %v", e)
	lastResourceUpdateTime = time.Now()
	if debouncedEvents == 0 {
	log.Debugf("This is the first debounced event")
	startDebounce = lastResourceUpdateTime
	}
	timeChan = time.After(debounceAfter)
	debouncedEvents++

如果持续有小于 debounceAfter 间隔的事件触发，会出现最终调用 pushConsulService2APIServer 方法的时间超过 debounceMax 的情况。这里是否有其他的考虑呢？

第二个是在这段代码中的条件判断

consul2istio/pkg/controller.go

Lines 123 to 138 in 4e4ed84

	if eventDelay >= debounceMax || quietTime >= debounceAfter {
	if debouncedEvents > 0 {
	pushCounter++
	log.Infof("Push debounce stable[%d] %d: %v since last change, %v since last push",
	pushCounter, debouncedEvents, quietTime, eventDelay)
	err := s.pushConsulService2APIServer()
	if err != nil {
	log.Errorf("Failed to synchronize consul services to Istio: %v", err)
	// Retry if failed
	s.pushChannel <- &ChangeEvent{}
	}
	debouncedEvents = 0
	}
	} else {
	timeChan = time.After(debounceAfter - quietTime)
	}

什么情况下会走到 else 中的分支呢？这里如果进入了 case <-timeChan，那必然是满足 eventDelay >= debounceMax || quietTime >= debounceAfter 的条件的。

基于以上，修改的代码如下

func (s *Controller) mainLoop(stop <-chan struct{}) {
	var timeChan <-chan time.Time
	var startDebounce time.Time
	var lastResourceUpdateTime time.Time
	pushCounter := 0
	debouncedEvents := 0

	for {
		select {
		case <-stop:
			break
		case e := <-s.pushChannel:
			log.Debugf("Receive event from push chanel : %v", e)
			lastResourceUpdateTime = time.Now()
			if debouncedEvents == 0 {
				log.Debugf("This is the first debounced event")
				startDebounce = lastResourceUpdateTime
			}
			eventDelay := time.Since(startDebounce)
			debouncedEvents++
			// it has been too long since the first debounced event or quiet enough since the last debounced event
			if eventDelay >= debounceMax {
				timeChan = time.After(0)
			} else {
				timeChan = time.After(debounceAfter)
			}
		case <-timeChan:
			log.Debugf("Receive event from time chanel")
			eventDelay := time.Since(startDebounce)
			quietTime := time.Since(lastResourceUpdateTime)
			pushCounter++
			log.Infof("Push debounce stable[%d] %d: %v since last change, %v since last push",
				pushCounter, debouncedEvents, quietTime, eventDelay)
			err := s.pushConsulService2APIServer()
			if err != nil {
				log.Errorf("Failed to synchronize consul services to Istio: %v", err)
				// Retry if failed
				s.pushChannel <- &ChangeEvent{}
			}
			debouncedEvents = 0
		}
	}
}