大量tcp拨号并发超时超过10000

Question

When the concurrency is raised to more than 10000, I got mass tcp dialog timeout.

$ go version

go version go1.12.1 linux/amd64

$ go env

GOARCH="amd64"
GOBIN="/home/zhoudazhuang/gobin/"
GOCACHE="/home/zhoudazhuang/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/zhoudazhuang/db11/jm/pro"
GOPROXY=""
GORACE=""
GOROOT="/home/zhoudazhuang/usr/local/go1.12.1/go"
GOTMPDIR=""
GOTOOLDIR="/home/zhoudazhuang/usr/local/go1.12.1/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build631445118=/tmp/go-build -gno-record-gcc-switches"

What did I do?

My tested code: Server:

func main() {
    l, err := net.Listen("tcp", ":8888")
    if err != nil {
        log.Println("listen error:", err)
        return
    }

    for {
        c, err := l.Accept()
        if err != nil {
            log.Println("accept error:", err)
            break
        }
        go c.Close()
        // start a new goroutine to handle
        // the new connection.
        //log.Println("accept a new connection")
        //go handleConn(c)
    }
}

Client:

package main

import (
    "fmt"
    "github.com/jessevdk/go-flags"
    "net"
    "os"
    "sync"
    "time"
)

var args struct {
    Addr string `short:"a"  required:"yes" description:"服务端地址"`
    Concurrence int `short:"c"  required:"yes" description:"并发请求数"`
    Count int `short:"t" required:"yes" description:"测试次数"`
}

func main() {
    argParser := flags.NewNamedParser("tcp_test", flags.PassDoubleDash)
    argParser.AddGroup("Mock parameters", "", &args)
    _, err := argParser.Parse()
    if err != nil {
        fmt.Println(err)
        argParser.WriteHelp(os.Stdout)
        os.Exit(1)
    }
    fmt.Printf("测试参数: %+v
",args)
    wg := sync.WaitGroup{}
    for j:=0; j<args.Count;j++ {
        for i:=0; i<args.Concurrence;i++{
            wg.Add(1)
            go func() {
                defer wg.Done()
                time.Sleep(time.Second*5)
                conn, err := net.DialTimeout("tcp", args.Addr, time.Second*3)
                if err != nil {
                    fmt.Printf("dialog err: %+v i为%d:
",err,j)
                    return
                }
                time.Sleep(time.Millisecond*10)
                conn.Close()
            }()
        }
    }
    fmt.Println("start wait")
    wg.Wait()
    fmt.Println("ok")
}

The cmd: ./Test -a 127.0.0.1:8888 -c 10000 -t 3

╰─># cat /proc/sys/net/ipv4/ip_local_port_range
4096 65535 ╰─># ulimit -a

core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 386849
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 10000000
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 1000000
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

What did you expect to see?

no tcp dial timeout.

What did you see instead?

dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:

Ref Issue:

issue