tmp.go

package main

import (
	"net"
	"sync"
	"syscall"
)

func setFdLimit(limit uint64) {
	var rLimit syscall.Rlimit
	err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rLimit)
	if err != nil {
		panic(err)
	}
	rLimit.Max = limit
	rLimit.Cur = limit
	err = syscall.Setrlimit(syscall.RLIMIT_NOFILE, &rLimit)
	if err != nil {
		panic(err)
	}
}

func main() {
	setFdLimit(16384 * 2)

	listener, err := net.Listen("tcp4", "127.0.0.1:0")
	if err != nil {
		panic(err)
	}
	go func() {
		var accepted []net.Conn
		for {
			c, err := listener.Accept()
			if err != nil {
				break
			}
			accepted = append(accepted, c)
		}
		for _, c := range accepted {
			c.Close()
		}
	}()

	var conns [16000]net.Conn
	for i := range conns {
		conns[i], err = net.Dial(listener.Addr().Network(), listener.Addr().String())
		if err != nil {
			panic(err)
		}
	}

	var ready, done sync.WaitGroup
	ready.Add(len(conns))
	done.Add(len(conns))

	for _, f := range conns {
		go func(f net.Conn) {
			defer done.Done()
			ready.Done()
			ready.Wait()

			f.Close()
		}(f)
	}
	done.Wait()
}