Golang（七）golang.org/x/time/rate 实现频率限制

// Allow is shorthand for AllowN(time.Now(), 1).
func (lim *Limiter) Allow() bool {
    return lim.AllowN(time.Now(), 1)
}

// AllowN reports whether n events may happen at time now.
// Use this method if you intend to drop / skip events that exceed the rate limit.
// Otherwise use Reserve or Wait.
func (lim *Limiter) AllowN(now time.Time, n int) bool {
    return lim.reserveN(now, n, 0).ok
}

lim.mu.Lock()
......
lim.mu.Unlock()
return r

if lim.limit == Inf {
    lim.mu.Unlock()
    return Reservation{
        ok:        true,
        lim:       lim,
        tokens:    n,
        timeToAct: now,
    }
}

// durationFromTokens is a unit conversion function from the number of tokens to the duration
// of time it takes to accumulate them at a rate of limit tokens per second.
func (limit Limit) durationFromTokens(tokens float64) time.Duration {
    seconds := tokens / float64(limit)
    return time.Nanosecond * time.Duration(1e9*seconds)
}

// tokensFromDuration is a unit conversion function from a time duration to the number of tokens
// which could be accumulated during that duration at a rate of limit tokens per second.
func (limit Limit) tokensFromDuration(d time.Duration) float64 {
    return d.Seconds() * float64(limit)
}

// Avoid making delta overflow below when last is very old.
maxElapsed := lim.limit.durationFromTokens(float64(lim.burst) - lim.tokens)
elapsed := now.Sub(last)
if elapsed > maxElapsed {
    elapsed = maxElapsed
}

// Calculate the new number of tokens, due to time that passed.
delta := lim.limit.tokensFromDuration(elapsed)
tokens := lim.tokens + delta
if burst := float64(lim.burst); tokens > burst {
    tokens = burst
}

// Calculate the remaining number of tokens resulting from the request.
tokens -= float64(n)
fmt.Printf("WangAo test: After sub n: tokens: %v\n", tokens)

// Calculate the wait duration
var waitDuration time.Duration
if tokens < 0 {
    waitDuration = lim.limit.durationFromTokens(-tokens)
}

// Decide result
ok := n <= lim.burst && waitDuration <= maxFutureReserve