Graceful stopping in Go [转]

• 英文: http://rcrowley.org/articles/golang-graceful-stop.html
• 中文: http://www.oschina.net/translate/golang-graceful-stop

原代码有几个地方有点问题:

• s.waitGroup.Add(1)需要在goroutine启动之前调用(否则可能丢失信息)
• signal.Notify的ch信道是阻塞的(signal.Notify不会阻塞发送信号),需要设置缓冲
• defer conn.Close()可能不会被执行到

调整后的代码:

package main

import (
	"log"
	"net"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"
)

// An uninteresting service.
type Service struct {
	ch        chan bool
	waitGroup *sync.WaitGroup
}

// Make a new Service.
func NewService() *Service {
	return &Service{
		ch:        make(chan bool),waitGroup: &sync.WaitGroup{},}
}

// Accept connections and spawn a goroutine to serve each one.  Stop listening
// if anything is received on the service's channel.
func (s *Service) Serve(listener *net.TCPListener) {
	s.waitGroup.Add(1)
	go func() {
		defer s.waitGroup.Done()
		for {
			select {
			case <-s.ch:
				log.Println("stopping listening on",listener.Addr())
				listener.Close()
				return
			default:
			}
			listener.SetDeadline(time.Now().Add(1e9))
			conn,err := listener.AcceptTCP()
			if nil != err {
				if opErr,ok := err.(*net.OpError); ok && opErr.Timeout() {
					continue
				}
				log.Println(err)
			}
			log.Println(conn.RemoteAddr(),"connected")
			s.serve(conn)
		}
	}()
}

// Stop the service by closing the service's channel.  Block until the service
// is really stopped.
func (s *Service) Stop() {
	close(s.ch)
	s.waitGroup.Wait()
}

// Serve a connection by reading and writing what was read.  That's right,this
// is an echo service.  Stop reading and writing if anything is received on the
// service's channel but only after writing what was read.
func (s *Service) serve(conn *net.TCPConn) {
	s.waitGroup.Add(1)
	go func() {
		defer s.waitGroup.Done()
		defer conn.Close()

		for {
			select {
			case <-s.ch:
				log.Println("disconnecting",conn.RemoteAddr())
				return
			default:
			}
			conn.SetDeadline(time.Now().Add(1e9))
			buf := make([]byte,4096)
			if _,err := conn.Read(buf); nil != err {
				if opErr,ok := err.(*net.OpError); ok && opErr.Timeout() {
					continue
				}
				log.Println(err)
				return
			}
			if _,err := conn.Write(buf); nil != err {
				log.Println(err)
				return
			}
		}
	}()
}

func main() {
	// Listen on 127.0.0.1:48879.  That's my favorite port number because in
	// hex 48879 is 0xBEEF.
	laddr,err := net.ResolveTCPAddr("tcp","127.0.0.1:48879")
	if nil != err {
		log.Fatalln(err)
	}
	listener,err := net.ListenTCP("tcp",laddr)
	if nil != err {
		log.Fatalln(err)
	}
	log.Println("listening on",listener.Addr())

	// Make a new service and send it into the background.
	service := NewService()
	service.Serve(listener)

	// Handle SIGINT and SIGTERM.
	ch := make(chan os.Signal,1)
	signal.Notify(ch,syscall.SIGINT,syscall.SIGTERM)
	log.Println(<-ch)

	// Stop the service gracefully.
	service.Stop()
}

（编辑：李大同）

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