emm

直接看原始碼即可，我一直用的是令牌桶

package main

import (
    "context"
    "fmt"
    "math"
    "sync"
    "time"
)

type Limit float64

const Inf = Limit(math.MaxFloat64)

func Every(interval time.Duration) Limit {
    if interval <= 0 {
        return Inf
    }

    return 1 / Limit(interval.Seconds())
}

type Limiter 
 
struct {
    limit Limit
    burst int

    mu sync.Mutex
    tokens float64
    last time.Time
    lastEvent time.Time
}

func (lim *Limiter) Limit() Limit {
    lim.mu.Lock()
    defer lim.mu.Unlock()
    return lim.limit
}

func (lim *Limiter) Burst() int {
    return lim.burst
}

func NewLimiter(r Limit, b 
 
int) *Limiter {
    return &Limiter{
        limit:r,
        burst:b,
    }
}

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

func (lim *Limiter) AllowN(now time.Time, n int) bool {
    return lim.reserveN(now, n, 0).ok
}

type Reservation struct {
    ok bool
    lim 
 
*Limiter
    tokens int
    timeToAct time.Time
    limit Limit
}

func (r *Reservation) OK() bool {
    return r.ok
}

func (r *Reservation) Delay() time.Duration {
    return r.DelayFrom(time.Now())
}

const InfDuration = time.Duration(1<<63 - 1)

func (r *Reservation) DelayFrom(now time.Time) time.Duration {
    if !r.ok {
        return InfDuration
    }
    delay := r.timeToAct.Sub(now)
    if delay < 0 {
        return 0
    }

    return delay
}

func (r *Reservation) Cancel() {
    r.CancelAt(time.Now())
    return
}

func (r *Reservation) CancelAt(now time.Time) {
    if !r.ok {
        return
    }

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

    if r.lim.limit == Inf || r.tokens == 0 || r.timeToAct.Before(now) {
        return
    }

    restoreTokens := float64(r.tokens) - r.limit.tokensFromDuration(r.lim.lastEvent.Sub(r.timeToAct))

    if restoreTokens < 0 {
        return
    }

    now, _, tokens := r.lim.advance(now)
    tokens += restoreTokens
    if burst := float64(r.lim.burst); tokens > burst {
        tokens = burst
    }
    r.lim.last = now
    r.lim.tokens = tokens

    if r.timeToAct == r.lim.lastEvent {
        preEvent := r.timeToAct.Add(r.limit.durationFromTokens(float64(-r.tokens)))
        if !preEvent.Before(now) {
            r.lim.lastEvent = preEvent
        }
    }

    return
}

func (lim *Limiter) Reserve() *Reservation {
    return lim.ReserveN(time.Now(), 1)
}

func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation {
    r := lim.reserveN(now, n, InfDuration)
    return &r
}

func (lim *Limiter) Wait(ctx context.Context) (err error) {
    return lim.WaitN(ctx, 1)
}

func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
    lim.mu.Lock()
    burst := lim.burst
    limit := lim.limit
    lim.mu.Unlock()

    if n > burst && limit != Inf {
        return fmt.Errorf("rate: wait (n=%d) exceeds limiter's burst %d", n, lim.burst)
    }

    select {
    case <-ctx.Done():
        return ctx.Err()
    default:
    }

    now := time.Now()
    waitLimit := InfDuration
    if deadline, ok := ctx.Deadline(); ok {
        waitLimit = deadline.Sub(now)
    }

    r := lim.reserveN(now, n, waitLimit)

    if !r.ok {
        return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
    }

    delay := r.DelayFrom(now)
    if delay == 0 {
        return nil
    }

    t := time.NewTimer(delay)
    defer t.Stop()
    select {
    case <-t.C:
        return nil
    case <-ctx.Done():
        r.Cancel()
        return ctx.Err()
    }
}

func (lim *Limiter) setLimit(newLimit Limit) {
    lim.SetLimitAt(time.Now(), newLimit)
}

func (lim *Limiter) SetLimitAt(now time.Time, newLimit Limit) {
    lim.mu.Lock()
    defer lim.mu.Unlock()

    now, _, tokens := lim.advance(now)

    lim.last = now
    lim.tokens = tokens
    lim.limit = newLimit

}

func (lim *Limiter) SetBurst(newBurst int) {
    lim.SetBurstAt(time.Now(), newBurst)
}

func (lim *Limiter) SetBurstAt(now time.Time, newBurst int) {
    lim.mu.Lock()
    defer lim.mu.Unlock()

    now, _, tokens := lim.advance(now)

    lim.last = now
    lim.tokens = tokens
    lim.burst = newBurst
}

func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
    lim.mu.Lock()

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

    now, last, tokens := lim.advance(now)

    tokens -= float64(n)

    var waitDuration time.Duration
    if tokens < 0 {
        waitDuration = lim.limit.durationFromTokens(-tokens)
    }

    ok := n <= lim.burst && waitDuration <= maxFutureReserve

    r := Reservation{
        ok:        ok,
        lim:       nil,
        limit:     lim.limit,
    }

    if ok {
        r.tokens = n
        r.timeToAct = now.Add(waitDuration)
    }

    if ok {
        lim.last = now
        lim.tokens = tokens
        lim.lastEvent = r.timeToAct
    } else {
        lim.last = last
    }

    lim.mu.Unlock()
    return r
}

func (lim *Limiter) advance(now time.Time) (newNow time.Time, newLast time.Time, newTokens float64) {
    last := lim.last
    if now.Before(last) {
        last = now
    }

    maxElapsed := lim.limit.durationFromTokens(float64(lim.burst) - lim.tokens)

    elapsed := now.Sub(last)
    if elapsed > maxElapsed {
        elapsed = maxElapsed
    }

    delta := lim.limit.tokensFromDuration(elapsed)

    tokens := lim.tokens + delta
    if burst := float64(lim.burst); tokens > burst {
        tokens = burst
    }
    return now, last, tokens
}

func (limit Limit) durationFromTokens(tokens float64) time.Duration {
    seconds := tokens / float64(limit)
    return time.Nanosecond * time.Duration(1e9*seconds)
}

func (limit Limit) tokensFromDuration(d time.Duration) float64 {
    sec := float64(d/time.Second) * float64(limit)
    naec := float64(d%time.Second) * float64(limit)
    return sec + naec/1e9
}

type Limiter struct {
  limit Limit // 放入桶的頻率   （Limit 為 float64型別）
  burst int   // 桶的大小

  mu     sync.Mutex
  tokens float64 // 當前桶內剩餘令牌個數
  last time.Time  // 最近取走token的時間
  lastEvent time.Time // 最近限流事件的時間
}

在令牌發放後，會被保留在Reservation 物件中，定義如下：

type Reservation struct {
  ok        bool  // 是否滿足條件分配到了tokens
  lim       *Limiter // 傳送令牌的限流器
  tokens    int   // tokens 的數量
  timeToAct time.Time  //  滿足令牌發放的時間
  limit Limit  // 令牌發放速度
}

https://github.com/chenyahui/AnnotatedCode/blob/master/go/x/time/rate/rate.go

https://segmentfault.com/a/1190000023033365