第一份代码

package main

import (
	"context"
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"time"
)

func main() {
	config := clientv3.Config{
		Endpoints:   []string{"127.0.0.1:2379"},
		DialTimeout: 5 * time.Millisecond,
	}
	client, err := clientv3.New(config)
	if err != nil {
		fmt.Println(err.Error())
	}
	lease := clientv3.NewLease(client)
	// 申请一个五秒过期的租约
	grant, err := lease.Grant(context.TODO(), 5)
	if err != nil {
		fmt.Println(err)
	}
	aliveChain, err := lease.KeepAlive(context.TODO(), grant.ID)


	kv := clientv3.NewKV(client)
	putValue, err := kv.Put(context.TODO(), "/cron/lock/lock1", "ticker", clientv3.WithLease(grant.ID))
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println("插入的revision＝", putValue.Header.Revision)
	for {
		value, err := kv.Get(context.TODO(), "/cron/lock/lock1")
		if err != nil {
			panic(err.Error())
		}
		if len(value.Kvs) == 0 {
			fmt.Println("key已经过期")
			break
		}
		time.Sleep(time.Second)
		fmt.Printf("获取的值=%v\n", value.Kvs)
	}
	// 续约协程
	go func() {
		for {
			select {
			case nn := <-aliveChain:
				if nn == nil {
					fmt.Println("续约失败", nn)
				} else {
					fmt.Println("续约中")
				}
			}
		}
	}()

}

这样的代码实现，只会打出 获取的值信息,类似如下输出

插入的revision＝ 38
获取的值=[key:"/cron/lock/lock1" create_revision:38 mod_revision:38 version:1 value:"ticker" lease:7587844330916674737 ]
获取的值=[key:"/cron/lock/lock1" create_revision:38 mod_revision:38 version:1 value:"ticker" lease:7587844330916674737 ]

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第二份代码

package main

import (
	"context"
	"fmt"
	"go.etcd.io/etcd/clientv3"
	"time"
)

func main() {
	config := clientv3.Config{
		Endpoints:   []string{"127.0.0.1:2379"},
		DialTimeout: 5 * time.Millisecond,
	}
	client, err := clientv3.New(config)
	if err != nil {
		fmt.Println(err.Error())
	}
	lease := clientv3.NewLease(client)
	// 申请一个五秒过期的租约
	grant, err := lease.Grant(context.TODO(), 5)
	if err != nil {
		fmt.Println(err)
	}
	aliveChain, err := lease.KeepAlive(context.TODO(), grant.ID)
	// 续约协程 （NOTE: 仅仅该函数的位置调整了）
	go func() {
		for {
			select {
			case nn := <-aliveChain:
				if nn == nil {
					fmt.Println("续约失败", nn)
				} else {
					fmt.Println("续约中")
				}
			}
		}
	}()

	kv := clientv3.NewKV(client)
	putValue, err := kv.Put(context.TODO(), "/cron/lock/lock1", "ticker", clientv3.WithLease(grant.ID))
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println("插入的revision＝", putValue.Header.Revision)
	for {
		value, err := kv.Get(context.TODO(), "/cron/lock/lock1")
		if err != nil {
			panic(err.Error())
		}
		if len(value.Kvs) == 0 {
			fmt.Println("key已经过期")
			break
		}
		time.Sleep(time.Second)
		fmt.Printf("获取的值=%v\n", value.Kvs)
	}
	

}

紧紧是调整了协程的代码位置，输出中会打出“续约中”，形如下列输出

续约中
插入的revision＝ 40
获取的值=[key:"/cron/lock/lock1" create_revision:40 mod_revision:40 version:1 value:"ticker" lease:7587844330916674753 ]
续约中
获取的值=[key:"/cron/lock/lock1" create_revision:40 mod_revision:40 version:1 value:"ticker" lease:7587844330916674753 ]
获取的值=[key:"/cron/lock/lock1" create_revision:40 mod_revision:40 version:1 value:"ticker" lease:7587844330916674753 ]

＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝分割线＝＝＝＝＝＝＝＝＝＝＝＝＝＝
问题： 为什么两份代码都能成功续约，都不会中断，但是第一份中没有打出“续约中”字样，仅仅是协程函数的代码位置的差异？
麻烦老师指点，多谢