uber-go/ratelimit 菜鸡求助

[bigHave]

uber 开源的限流算法，代码不多，尝试理解但是没怎么理解。有没有大佬指点一二.主要不理解的点在于这个 for 循环

// Take blocks to ensure that the time spent between multiple
// Take calls is on average time.Second/rate.
func (t *limiter) Take() time.Time {
	newState := state{}
	taken := false
	for !taken {
		now := t.clock.Now()

		previousStatePointer := atomic.LoadPointer(&t.state)
		oldState := (*state)(previousStatePointer)

		newState = state{}
		newState.last = now

		// If this is our first request, then we allow it.
		if oldState.last.IsZero() {
			taken = atomic.CompareAndSwapPointer(&t.state, previousStatePointer, unsafe.Pointer(&newState))
			continue
		}

		// sleepFor calculates how much time we should sleep based on
		// the perRequest budget and how long the last request took.
		// Since the request may take longer than the budget, this number
		// can get negative, and is summed across requests.
		newState.sleepFor += t.perRequest - now.Sub(oldState.last)
		// We shouldn't allow sleepFor to get too negative, since it would mean that
		// a service that slowed down a lot for a short period of time would get
		// a much higher RPS following that.
		if newState.sleepFor < t.maxSlack {
			newState.sleepFor = t.maxSlack
		}
		if newState.sleepFor > 0 {
			newState.last = newState.last.Add(newState.sleepFor)
		}
		taken = atomic.CompareAndSwapPointer(&t.state, previousStatePointer, unsafe.Pointer(&newState))
	}
	t.clock.Sleep(newState.sleepFor)
	return newState.last
}

[CRVV]

var counter int64

然后如果有多个线程执行下面这个循环，每次 break 都会给 counter 加一
for {
counter0 := atomic.LoadInt64(&counter)
if atomic.CompareAndSwap(&counter, counter0, counter+1) {
break
}
}

这种就是所谓的 lock-free，把它写成用 lock 的形式，再把那几个 if 去掉，这个函数其实就是

func (t *limiter) Take() time.Time {

mutex.Lock()

oldState := t.state
newState = state{}
now := t.clock.Now()
newState.last = now
newState.sleepFor += t.perRequest - now.Sub(oldState.last)

t.state = &newState
mutex.Unlock()

t.clock.Sleep(newState.sleepFor)
return newState.last
}

然后应该很好懂了

[bigHave]

@CRVV 感谢。第一次在 V2EX 发帖就得到了高效帮助，太棒了