golang官方實現如何對httpserver做頻率限制(最大連接數限制)

 

一般海量處理服務，都會對服務做個最大連接數限制，超過該限制之后，拒絕服務，避免發生雪崩，壓壞服務。

使用golang來編寫httpserver時，如何進行呢？官方已經有實現好的包。

使用示例：

 

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

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.................

 

 

源碼如下(url : https://github.com/golang/net/blob/master/netutil/listen.go)，基本思路就是為連接數計數，通過make chan來建立一個最大連接數的channel, 每次accept就+1，close時候就-1. 當到達最大連接數時，就等待空閑連接出來之后再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{l, make(chan struct{}, n)}
}

type limitListener struct {
    net.Listener
    sem chan struct{}
}

func (l *limitListener) acquire() { l.sem <- struct{}{} } func (l *limitListener) release() { <-l.sem }

func (l *limitListener) Accept() (net.Conn, error) {
    //若connect chan已滿,則會阻塞在此處
    l.acquire()
    c, err := l.Listener.Accept()
    if err != nil {
        l.release()
        return nil, err
    }
    return &limitListenerConn{Conn: c, release: l.release}, nil
}

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

func (l *limitListenerConn) Close() error {
    err := l.Conn.Close()
   l.releaseOnce.Do(l.release) return err
}