Go语言小技巧(2) - 定时任务

K8S运用了大量定时任务，学习下实现方法

go wait.Until(kl.syncNetworkUtil, 1*time.Minute, wait.NeverStop)

code

k8s.io\apimachinery\pkg\util\wait\wait.go

// Until loops until stop channel is closed, running f every period.
//
// Until is syntactic sugar on top of JitterUntil with zero jitter factor and
// with sliding = true (which means the timer for period starts after the f
// completes).
func Until(f func(), period time.Duration, stopCh <-chan struct{}) {
    JitterUntil(f, period, 0.0, true, stopCh)
}

// JitterUntil loops until stop channel is closed, running f every period.
//
// If jitterFactor is positive, the period is jittered before every run of f.
// If jitterFactor is not positive, the period is unchanged and not jittered.
//
// If sliding is true, the period is computed after f runs. If it is false then
// period includes the runtime for f.
//
// Close stopCh to stop. f may not be invoked if stop channel is already
// closed. Pass NeverStop to if you don't want it stop.
func JitterUntil(f func(), period time.Duration, jitterFactor float64, sliding bool, stopCh <-chan struct{}) {
    var t *time.Timer
    var sawTimeout bool

    for {
        select {
        case <-stopCh:
            return
        default:
        }

        jitteredPeriod := period
        if jitterFactor > 0.0 {
            jitteredPeriod = Jitter(period, jitterFactor)
        }
        
        // 任务开始前计时
        if !sliding {
            t = resetOrReuseTimer(t, jitteredPeriod, sawTimeout)
        }

        func() {
            // recover panic
            defer runtime.HandleCrash()
            f()
        }()
        
        // 任务完成后计时
        if sliding {
            t = resetOrReuseTimer(t, jitteredPeriod, sawTimeout)
        }

        // NOTE: b/c there is no priority selection in golang
        // it is possible for this to race, meaning we could
        // trigger t.C and stopCh, and t.C select falls through.
        // In order to mitigate we re-check stopCh at the beginning
        // of every loop to prevent extra executions of f().
        select {
        case <-stopCh:
            return
        case <-t.C:
            sawTimeout = true
        }
    }
}

// Jitter returns a time.Duration between duration and duration + maxFactor *
// duration.
//
// This allows clients to avoid converging on periodic behavior. If maxFactor
// is 0.0, a suggested default value will be chosen.
func Jitter(duration time.Duration, maxFactor float64) time.Duration {
    if maxFactor <= 0.0 {
        maxFactor = 1.0
    }
    wait := duration + time.Duration(rand.Float64()*maxFactor*float64(duration))
    return wait
}

// resetOrReuseTimer avoids allocating a new timer if one is already in use.
// Not safe for multiple threads.
func resetOrReuseTimer(t *time.Timer, d time.Duration, sawTimeout bool) *time.Timer {
    if t == nil {
        return time.NewTimer(d)
    }
    if !t.Stop() && !sawTimeout {
        <-t.C
    }
    t.Reset(d)
    return t
}