详解Golang实现请求限流的几种办法

简单的并发控制

 

利用 channel 的缓冲设定，我们就可以来实现并发的限制。我们只要在执行并发的同时，往一个带有缓冲的 channel 里写入点东西（随便写啥，内容不重要）。让并发的 goroutine在执行完成后把这个 channel 里的东西给读走。这样整个并发的数量就讲控制在这个 channel的缓冲区大小上。

比如我们可以用一个 bool 类型的带缓冲 channel 作为并发限制的计数器。

chLimit := make(chan bool, 1)

然后在并发执行的地方，每创建一个新的 goroutine，都往 chLimit 里塞个东西。

for i, sleeptime := range input {
    chs[i] = make(chan string, 1)
    chLimit <- true
    go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
}

这里通过 go 关键字并发执行的是新构造的函数。他在执行完后，会把 chLimit的缓冲区里给消费掉一个。

limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
    Run(task_id, sleeptime, timeout, ch)
    <-chLimit
}

这样一来，当创建的 goroutine 数量到达 chLimit 的缓冲区上限后。主 goroutine 就挂起阻塞了，直到这些 goroutine 执行完毕，消费掉了 chLimit 缓冲区中的数据，程序才会继续创建新的 goroutine 。我们并发数量限制的目的也就达到了。

以下是完整代码：

package main

import (
    "fmt"
    "time"
)

func Run(task_id, sleeptime, timeout int, ch chan string) {
    ch_run := make(chan string)
    go run(task_id, sleeptime, ch_run)
    select {
    case re := <-ch_run:
        ch <- re
    case <-time.After(time.Duration(timeout) * time.Second):
        re := fmt.Sprintf("task id %d , timeout", task_id)
        ch <- re
    }
}

func run(task_id, sleeptime int, ch chan string) {

    time.Sleep(time.Duration(sleeptime) * time.Second)
    ch <- fmt.Sprintf("task id %d , sleep %d second", task_id, sleeptime)
    return
}

func main() {
    input := []int{3, 2, 1}
    timeout := 2
    chLimit := make(chan bool, 1)
    chs := make([]chan string, len(input))
    limitFunc := func(chLimit chan bool, ch chan string, task_id, sleeptime, timeout int) {
        Run(task_id, sleeptime, timeout, ch)
        <-chLimit
    }
    startTime := time.Now()
    fmt.Println("Multirun start")
    for i, sleeptime := range input {
        chs[i] = make(chan string, 1)
        chLimit <- true
        go limitFunc(chLimit, chs[i], i, sleeptime, timeout)
    }

    for _, ch := range chs {
        fmt.Println(<-ch)
    }
    endTime := time.Now()
    fmt.Printf("Multissh finished. Process time %s. Number of task is %d", endTime.Sub(startTime), len(input))
}

运行结果：

Multirun start
task id 0 , timeout
task id 1 , timeout
task id 2 , sleep 1 second
Multissh finished. Process time 5s. Number of task is 3

如果修改并发限制为2：

chLimit := make(chan bool, 2)

运行结果：

Multirun start
task id 0 , timeout
task id 1 , timeout
task id 2 , sleep 1 second
Multissh finished. Process time 3s. Number of task is 3

使用计数器实现请求限流

 

限流的要求是在指定的时间间隔内，server 最多只能服务指定数量的请求。实现的原理是我们启动一个计数器，每次服务请求会把计数器加一，同时到达指定的时间间隔后会把计数器清零；这个计数器的实现代码如下所示：

type RequestLimitService struct {
 Interval time.Duration
 MaxCount int
 Lock     sync.Mutex
 ReqCount int
}

func NewRequestLimitService(interval time.Duration, maxCnt int) *RequestLimitService {
 reqLimit := &RequestLimitService{
  Interval: interval,
  MaxCount: maxCnt,
 }

 go func() {
  ticker := time.NewTicker(interval)
  for {
   <-ticker.C
   reqLimit.Lock.Lock()
   fmt.Println("Reset Count...")
   reqLimit.ReqCount = 0
   reqLimit.Lock.Unlock()
  }
 }()

 return reqLimit
}

func (reqLimit *RequestLimitService) Increase() {
 reqLimit.Lock.Lock()
 defer reqLimit.Lock.Unlock()

 reqLimit.ReqCount += 1
}

func (reqLimit *RequestLimitService) IsAvailable() bool {
 reqLimit.Lock.Lock()
 defer reqLimit.Lock.Unlock()

 return reqLimit.ReqCount < reqLimit.MaxCount
}

在服务请求的时候, 我们会对当前计数器和阈值进行比较，只有未超过阈值时才进行服务：

var RequestLimit = NewRequestLimitService(10 * time.Second, 5)

func helloHandler(w http.ResponseWriter, r *http.Request) {
 if RequestLimit.IsAvailable() {
  RequestLimit.Increase()
  fmt.Println(RequestLimit.ReqCount)
  io.WriteString(w, "Hello world!\n")
 } else {
  fmt.Println("Reach request limiting!")
  io.WriteString(w, "Reach request limit!\n")
 }
}

func main() {
 fmt.Println("Server Started!")
 http.HandleFunc("/", helloHandler)
 http.ListenAndServe(":8000", nil)
}

完整代码url：https://github.com/hiberabyss/JustDoIt/blob/master/RequestLimit/request_limit.go

使用golang官方包实现httpserver频率限制

 

使用golang来编写httpserver时，可以使用官方已经有实现好的包：

import(
    "fmt"
    "net"
    "golang.org/x/net/netutil"
)

func main() {
    l, err := net.Listen("tcp", "127.0.0.1:0")
    if err != nil {
        fmt.Fatalf("Listen: %v", err)
    }
    defer l.Close()
    l = LimitListener(l, max)

    http.Serve(l, http.HandlerFunc())

    //bla bla bla.................
}

源码如下(url : https://github.com/golang/net/blob/master/netutil/listen.go)，基本思路就是为连接数计数，通过make chan来建立一个最大连接数的channel, 每次accept就+1，close时候就-1. 当到达最大连接数时，就等待空闲连接出来之后再accept。

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package netutil provides network utility functions, complementing the more
// common ones in the net package.
package netutil // import "golang.org/x/net/netutil"

import (
    "net"
 "sync"
)

// LimitListener returns a Listener that accepts at most n simultaneous
// connections from the provided Listener.
func LimitListener(l net.Listener, n int) net.Listener {
 return &limitListener{
  Listener: l,
  sem:      make(chan struct{}, n),
  done:     make(chan struct{}),
 }
}

type limitListener struct {
 net.Listener
 sem       chan struct{}
 closeOnce sync.Once     // ensures the done chan is only closed once
 done      chan struct{} // no values sent; closed when Close is called
}

// acquire acquires the limiting semaphore. Returns true if successfully
// accquired, false if the listener is closed and the semaphore is not
// acquired.
func (l *limitListener) acquire() bool {
 select {
 case <-l.done:
  return false
 case l.sem <- struct{}{}:
  return true
 }
}
func (l *limitListener) release() { <-l.sem }

func (l *limitListener) Accept() (net.Conn, error) {
    //如果sem满了，就会阻塞在这
 acquired := l.acquire()
 // If the semaphore isn't acquired because the listener was closed, expect
 // that this call to accept won't block, but immediately return an error.
 c, err := l.Listener.Accept()
 if err != nil {
  if acquired {
   l.release()
  }
  return nil, err
 }
 return &limitListenerConn{Conn: c, release: l.release}, nil
}

func (l *limitListener) Close() error {
 err := l.Listener.Close()
 l.closeOnce.Do(func() { close(l.done) })
 return err
}

type limitListenerConn struct {
 net.Conn
 releaseOnce sync.Once
 release     func()
}

func (l *limitListenerConn) Close() error {
 err := l.Conn.Close()
    //close时释放占用的sem
 l.releaseOnce.Do(l.release)
 return err
}

使用Token Bucket（令牌桶算法）实现请求限流

 

在开发高并发系统时有三把利器用来保护系统：缓存、降级和限流!为了保证在业务高峰期，线上系统也能保证一定的弹性和稳定性，最有效的方案就是进行服务降级了，而限流就是降级系统最常采用的方案之一。

这里为大家推荐一个开源库https://github.com/didip/tollbooth，但是，如果您想要一些简单的、轻量级的或者只是想要学习的东西，实现自己的中间件来处理速率限制并不困难。今天我们就来聊聊如何实现自己的一个限流中间件

首先我们需要安装一个提供了 Token bucket (令牌桶算法)的依赖包，上面提到的toolbooth 的实现也是基于它实现的：

$ go get golang.org/x/time/rate

先看Demo代码的实现：

package main

import (
    "net/http"
    "golang.org/x/time/rate"
)

var limiter = rate.NewLimiter(2, 5)
func limit(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if limiter.Allow() == false {
            http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
            return
        }
        next.ServeHTTP(w, r)
    })
}

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", okHandler)
    // Wrap the servemux with the limit middleware.
    http.ListenAndServe(":4000", limit(mux))
}

func okHandler(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("OK"))
}

然后看看 rate.NewLimiter的源码：

算法描述：用户配置的平均发送速率为r，则每隔1/r秒一个令牌被加入到桶中（每秒会有r个令牌放入桶中），桶中最多可以存放b个令牌。如果令牌到达时令牌桶已经满了，那么这个令牌会被丢弃；

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package rate provides a rate limiter.
package rate

import (
 "fmt"
 "math"
 "sync"
 "time"

 "golang.org/x/net/context"
)

// Limit defines the maximum frequency of some events.
// Limit is represented as number of events per second.
// A zero Limit allows no events.
type Limit float64

// Inf is the infinite rate limit; it allows all events (even if burst is zero).
const Inf = Limit(math.MaxFloat64)

// Every converts a minimum time interval between events to a Limit.
func Every(interval time.Duration) Limit {
 if interval <= 0 {
  return Inf
 }
 return 1 / Limit(interval.Seconds())
}

// A Limiter controls how frequently events are allowed to happen.
// It implements a "token bucket" of size b, initially full and refilled
// at rate r tokens per second.
// Informally, in any large enough time interval, the Limiter limits the
// rate to r tokens per second, with a maximum burst size of b events.
// As a special case, if r == Inf (the infinite rate), b is ignored.
// See https://en.wikipedia.org/wiki/Token_bucket for more about token buckets.
//
// The zero value is a valid Limiter, but it will reject all events.
// Use NewLimiter to create non-zero Limiters.
//
// Limiter has three main methods, Allow, Reserve, and Wait.
// Most callers should use Wait.
//
// Each of the three methods consumes a single token.
// They differ in their behavior when no token is available.
// If no token is available, Allow returns false.
// If no token is available, Reserve returns a reservation for a future token
// and the amount of time the caller must wait before using it.
// If no token is available, Wait blocks until one can be obtained
// or its associated context.Context is canceled.
//
// The methods AllowN, ReserveN, and WaitN consume n tokens.
type Limiter struct {
 //maximum token, token num per second
 limit Limit
 //burst field, max token num
 burst int
 mu    sync.Mutex
 //tokens num, change
 tokens float64
 // last is the last time the limiter's tokens field was updated
 last time.Time
 // lastEvent is the latest time of a rate-limited event (past or future)
 lastEvent time.Time
}

// Limit returns the maximum overall event rate.
func (lim *Limiter) Limit() Limit {
 lim.mu.Lock()
 defer lim.mu.Unlock()
 return lim.limit
}

// Burst returns the maximum burst size. Burst is the maximum number of tokens
// that can be consumed in a single call to Allow, Reserve, or Wait, so higher
// Burst values allow more events to happen at once.
// A zero Burst allows no events, unless limit == Inf.
func (lim *Limiter) Burst() int {
 return lim.burst
}

// NewLimiter returns a new Limiter that allows events up to rate r and permits
// bursts of at most b tokens.
func NewLimiter(r Limit, b int) *Limiter {
 return &Limiter{
  limit: r,
  burst: b,
 }
}

// 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
}

// A Reservation holds information about events that are permitted by a Limiter to happen after a delay.
// A Reservation may be canceled, which may enable the Limiter to permit additional events.
type Reservation struct {
 ok     bool
 lim    *Limiter
 tokens int
 //This is the time to action
 timeToAct time.Time
 // This is the Limit at reservation time, it can change later.
 limit Limit
}

// OK returns whether the limiter can provide the requested number of tokens
// within the maximum wait time.  If OK is false, Delay returns InfDuration, and
// Cancel does nothing.
func (r *Reservation) OK() bool {
 return r.ok
}

// Delay is shorthand for DelayFrom(time.Now()).
func (r *Reservation) Delay() time.Duration {
 return r.DelayFrom(time.Now())
}

// InfDuration is the duration returned by Delay when a Reservation is not OK.
const InfDuration = time.Duration(1<<63 - 1)

// DelayFrom returns the duration for which the reservation holder must wait
// before taking the reserved action.  Zero duration means act immediately.
// InfDuration means the limiter cannot grant the tokens requested in this
// Reservation within the maximum wait time.
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
}

// Cancel is shorthand for CancelAt(time.Now()).
func (r *Reservation) Cancel() {
 r.CancelAt(time.Now())
 return
}

// CancelAt indicates that the reservation holder will not perform the reserved action
// and reverses the effects of this Reservation on the rate limit as much as possible,
// considering that other reservations may have already been made.
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
 }
 // calculate tokens to restore
 // The duration between lim.lastEvent and r.timeToAct tells us how many tokens were reserved
 // after r was obtained. These tokens should not be restored.
 restoreTokens := float64(r.tokens) - r.limit.tokensFromDuration(r.lim.lastEvent.Sub(r.timeToAct))
 if restoreTokens <= 0 {
  return
 }
 // advance time to now
 now, _, tokens := r.lim.advance(now)
 // calculate new number of tokens
 tokens += restoreTokens
 if burst := float64(r.lim.burst); tokens > burst {
  tokens = burst
 }
 // update state
 r.lim.last = now
 r.lim.tokens = tokens
 if r.timeToAct == r.lim.lastEvent {
  prevEvent := r.timeToAct.Add(r.limit.durationFromTokens(float64(-r.tokens)))
  if !prevEvent.Before(now) {
   r.lim.lastEvent = prevEvent
  }
 }
 return
}

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

// ReserveN returns a Reservation that indicates how long the caller must wait before n events happen.
// The Limiter takes this Reservation into account when allowing future events.
// ReserveN returns false if n exceeds the Limiter's burst size.
// Usage example:
//   r, ok := lim.ReserveN(time.Now(), 1)
//   if !ok {
//     // Not allowed to act! Did you remember to set lim.burst to be > 0 ?
//   }
//   time.Sleep(r.Delay())
//   Act()
// Use this method if you wish to wait and slow down in accordance with the rate limit without dropping events.
// If you need to respect a deadline or cancel the delay, use Wait instead.
// To drop or skip events exceeding rate limit, use Allow instead.
func (lim *Limiter) ReserveN(now time.Time, n int) *Reservation {
 r := lim.reserveN(now, n, InfDuration)
 return &r
}

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

// WaitN blocks until lim permits n events to happen.
// It returns an error if n exceeds the Limiter's burst size, the Context is
// canceled, or the expected wait time exceeds the Context's Deadline.
func (lim *Limiter) WaitN(ctx context.Context, n int) (err error) {
 if n > lim.burst {
  return fmt.Errorf("rate: Wait(n=%d) exceeds limiter's burst %d", n, lim.burst)
 }
 // Check if ctx is already cancelled
 select {
 case <-ctx.Done():
  return ctx.Err()
 default:
 }
 // Determine wait limit
 now := time.Now()
 waitLimit := InfDuration
 if deadline, ok := ctx.Deadline(); ok {
  waitLimit = deadline.Sub(now)
 }
 // Reserve
 r := lim.reserveN(now, n, waitLimit)
 if !r.ok {
  return fmt.Errorf("rate: Wait(n=%d) would exceed context deadline", n)
 }
 // Wait
 t := time.NewTimer(r.DelayFrom(now))
 defer t.Stop()
 select {
 case <-t.C:
  // We can proceed.
  return nil
 case <-ctx.Done():
  // Context was canceled before we could proceed.  Cancel the
  // reservation, which may permit other events to proceed sooner.
  r.Cancel()
  return ctx.Err()
 }
}

// SetLimit is shorthand for SetLimitAt(time.Now(), newLimit).
func (lim *Limiter) SetLimit(newLimit Limit) {
 lim.SetLimitAt(time.Now(), newLimit)
}

// SetLimitAt sets a new Limit for the limiter. The new Limit, and Burst, may be violated
// or underutilized by those which reserved (using Reserve or Wait) but did not yet act
// before SetLimitAt was called.
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
}

// reserveN is a helper method for AllowN, ReserveN, and WaitN.
// maxFutureReserve specifies the maximum reservation wait duration allowed.
// reserveN returns Reservation, not *Reservation, to avoid allocation in AllowN and WaitN.
func (lim *Limiter) reserveN(now time.Time, n int, maxFutureReserve time.Duration) Reservation {
 lim.mu.Lock()
 defer lim.mu.Unlock()
 if lim.limit == Inf {
  return Reservation{
   ok:        true,
   lim:       lim,
   tokens:    n,
   timeToAct: now,
  }
 }
 now, last, tokens := lim.advance(now)
 // Calculate the remaining number of tokens resulting from the request.
 tokens -= float64(n)
 // Calculate the wait duration
 var waitDuration time.Duration
 if tokens < 0 {
  waitDuration = lim.limit.durationFromTokens(-tokens)
 }
 // Decide result
 ok := n <= lim.burst && waitDuration <= maxFutureReserve
 // Prepare reservation
 r := Reservation{
  ok:    ok,
  lim:   lim,
  limit: lim.limit,
 }
 if ok {
  r.tokens = n
  r.timeToAct = now.Add(waitDuration)
 }
 // Update state
 if ok {
  lim.last = now
  lim.tokens = tokens
  lim.lastEvent = r.timeToAct
 } else {
  lim.last = last
 }
 return r
}

// advance calculates and returns an updated state for lim resulting from the passage of time.
// lim is not changed.
func (lim *Limiter) advance(now time.Time) (newNow time.Time, newLast time.Time, newTokens float64) {
 last := lim.last
 if now.Before(last) {
  last = now
 }
 // 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
 }
 return now, last, tokens
}

// 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)
}

虽然在某些情况下使用单个全局速率限制器非常有用，但另一种常见情况是基于IP地址或API密钥等标识符为每个用户实施速率限制器。我们将使用IP地址作为标识符。简单实现代码如下：

package main
import (
    "net/http"
    "sync"
    "time"
    "golang.org/x/time/rate"
)
// Create a custom visitor struct which holds the rate limiter for each
// visitor and the last time that the visitor was seen.
type visitor struct {
    limiter  *rate.Limiter
    lastSeen time.Time
}
// Change the the map to hold values of the type visitor.
var visitors = make(map[string]*visitor)
var mtx sync.Mutex
// Run a background goroutine to remove old entries from the visitors map.
func init() {
    go cleanupVisitors()
}
func addVisitor(ip string) *rate.Limiter {
    limiter := rate.NewLimiter(2, 5)
    mtx.Lock()
    // Include the current time when creating a new visitor.
    visitors[ip] = &visitor{limiter, time.Now()}
    mtx.Unlock()
    return limiter
}
func getVisitor(ip string) *rate.Limiter {
    mtx.Lock()
    v, exists := visitors[ip]
    if !exists {
        mtx.Unlock()
        return addVisitor(ip)
    }
    // Update the last seen time for the visitor.
    v.lastSeen = time.Now()
    mtx.Unlock()
    return v.limiter
}
// Every minute check the map for visitors that haven't been seen for
// more than 3 minutes and delete the entries.
func cleanupVisitors() {
    for {
        time.Sleep(time.Minute)
        mtx.Lock()
        for ip, v := range visitors {
            if time.Now().Sub(v.lastSeen) > 3*time.Minute {
                delete(visitors, ip)
            }
        }
        mtx.Unlock()
    }
}
func limit(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        limiter := getVisitor(r.RemoteAddr)
        if limiter.Allow() == false {
            http.Error(w, http.StatusText(429), http.StatusTooManyRequests)
            return
        }
        next.ServeHTTP(w, r)
    })
}

到此这篇关于详解Golang实现请求限流的几种办法的文章就介绍到这了,更多相关Golang 请求限流内容请搜索服务器之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持服务器之家！ 

原文链接：https://blog.csdn.net/micl200110041/article/details/82013032