服务做个最大连接数限制

àì夳堔傛蜴生んèń 2022-07-16 04:16 241阅读 0赞

一般海量处理服务，都会对服务做个最大连接数限制，超过该限制之后，拒绝服务，避免发生雪崩，压坏服务。

使用golang来编写httpserver时，如何进行呢？官方已经有实现好的包。

使用示例：

![复制代码][copycode.gif]

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

![复制代码][copycode.gif]

源码如下(url :[ https://github.com/golang/net/blob/master/netutil/listen.go][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。

![复制代码][copycode.gif]

// 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已满,则会阻塞在此处
       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
    }

![复制代码][copycode.gif]

[copycode.gif]: /images/20220716/b9987003a6cc43d5b7cbda8ddd09b7af.png
[https_github.com_golang_net_blob_master_netutil_listen.go]: https://github.com/golang/net/blob/master/netutil/listen.go