目录
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)
- })
- }
转载: https://blog.csdn.net/micl200110041/article/details/82013032