a graceful http demo.

grafefulHttp.go

package main

import (
	"context"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"syscall"
	"time"
)

var ln net.Listener
var srv http.Server

func main() {
	fmt.Println("start")
	fmt.Printf("%v\n", os.Environ())
	http.HandleFunc("/hello", getPidHandle)
	Addr := ":8080"
	var err error
	if os.Getenv("_GRACEFUL") == "true" {
		fd := os.NewFile(3, "")
		ln, err = net.FileListener(fd)
		if err != nil {
			log.Fatal(err)
		}
	} else {
		ln, err = net.Listen("tcp", Addr)
		if err != nil {
			log.Fatal(err)
		}
	}
	go srv.Serve(ln)
	sig := make(chan os.Signal, 1)
	signal.Notify(sig, syscall.SIGUSR2)
	s := <-sig
	for {
		switch s {
		case syscall.SIGUSR2:
			fmt.Printf("%v\n", s)
			reload()
			stop()
			return
		}
	}
	fmt.Println("Exiting")
}

func getPidHandle(w http.ResponseWriter, r *http.Request) {
	io.WriteString(w, "Hello, world!\n"+fmt.Sprintf("%d\n", os.Getpid()))
}

func reload() {
	tcp, ok := ln.(*net.TCPListener)
	if !ok {
		log.Fatal("tcp listener tcp not ok")
	}
	f, err := tcp.File()
	if err != nil {
		log.Fatal(err)
	}
	cmd := exec.Command(os.Args[0])
	os.Setenv("_GRACEFUL", "true")
	cmd.ExtraFiles = []*os.File{f}
	err = cmd.Start()
	if err != nil {
		log.Fatal(err)
	}
}

func stop() {
	// shutdown old service
	ctx, cancleHandle := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancleHandle()
	err := srv.Shutdown(ctx)
	if err != nil {
		log.Fatal(err)
	}
	time.Sleep(6 * time.Second)
}