Handle 1 million concurrent connections with 50 lines Go code

[Jack Li]

Hi group,

I am going through this page: https://studygolang.com/articles/22820 , It claims that the 50 lines of Go code handles 1 million concurrent connections from network clients, on 1 single server machine with a 4-Core CPU and 16G memory.

Does the package net already utilize IO Multiplexing internally, like epoll (epoll_create, epoll_ctl, epoll_wait)? So I can just use package net and gain the epoll ability automatically without calling epoll apis manually in Go?

Thanks

Server:

```

package main

import (

    "fmt"

    "net"

    "os"

    "time"

)

var array []byte = make([]byte, 10)

func checkError(err error, info string) (res bool) {

    if err != nil {

        fmt.Println(info + "  " + err.Error())

        return false

    }

    return true

}

func Handler(conn net.Conn) {

    for {

        _, err := conn.Write(array)

        if err != nil {

            return

        }

        time.Sleep(10 * time.Second)

    }

}

func main() {

    for i := 0; i < 10; i += 1 {

        array[i] = 'a'

    }

    service := ":8888"

    tcpAddr, _ := net.ResolveTCPAddr("tcp4", service)

    l, _ := net.ListenTCP("tcp", tcpAddr)

    for {

        conn, err := l.Accept()

        if err != nil {

            fmt.Printf("accept error, err=%s\n", err.Error())

            os.Exit(1)

        }

        go Handler(conn)

    }

}

```

Client:

```

package main

import (

    "flag"

    "fmt"

    "net"

    "os"

    "time"

)

var RemoteAddr *string

var ConcurNum *int

var LocalAddr *string

func init() {

    RemoteAddr = flag.String("remote-ip", "127.0.0.1", "ip addr of remote server")

    ConcurNum = flag.Int("concurrent-num", 100, "concurrent number of client")

    LocalAddr = flag.String("local-ip", "0.0.0.0", "ip addr of remote server")

}

func consume() {

    laddr := &net.TCPAddr{IP: net.ParseIP(*LocalAddr)}

    var dialer net.Dialer

    dialer.LocalAddr = laddr

    conn, err := dialer.Dial("tcp", *RemoteAddr+":8888")

    if err != nil {

        fmt.Println("dial failed:", err)

        os.Exit(1)

    }

    defer conn.Close()

    buffer := make([]byte, 512)

    for {

        _, err2 := conn.Read(buffer)

        if err2 != nil {

            fmt.Println("Read failed:", err2)

            return

        }

        //  fmt.Println("count:", n, "msg:", string(buffer))

    }

}

func main() {

    flag.Parse()

    for i := 0; i < *ConcurNum; i++ {

        go consume()

    }

    time.Sleep(3600 * time.Second)

}

```

[Amnon]

Yes, the Go runtime does use epoll internally and schedules gorountines when their data is available. 
See https://github.com/golang/go/blob/17b2fb1b656a275906b5071c562439d50a27f167/src/runtime/netpoll_epoll.go
It does scale nicely and can handle tens of thousands or even hundreds of thousands of concurrent connections, without the "Thundering 
Herd" type behaviour which one would expect from such systems.
I have not tried it with millions of connection, but if you are interested, then run a test, but the consume side of your test will run out of ports.

[Ian Lance Taylor]

On Wed, Apr 6, 2022 at 6:43 AM 'Jack Li' via golang-nuts
<golan...@googlegroups.com> wrote:
>
> I am going through this page: https://studygolang.com/articles/22820 , It claims that the 50 lines of Go code handles 1 million concurrent connections from network clients, on 1 single server machine with a 4-Core CPU and 16G memory.
>
> Does the package net already utilize IO Multiplexing internally, like epoll (epoll_create, epoll_ctl, epoll_wait)? So I can just use package net and gain the epoll ability automatically without calling epoll apis manually in Go?

I didn't read your program, but, yes, the net package uses epoll
internally. There is no need to call epoll yourself.

Ian

[Robert Engels]

Yes. Go uses “green threads” with its own scheduler and uses facilities like epoll under the covers. 

On Apr 6, 2022, at 8:43 AM, 'Jack Li' via golang-nuts <golan...@googlegroups.com> wrote:



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