You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.go
    path of file: ./repos/learning/golang/practice/go-crontab/gopath/src/github.com/owenliang/prepare/etcd_usage/demo9
    
    the code of the file until where you have to start completion: package main

import (
	"github.com/coreos/etcd/clientv3"
	"time"
	"fmt"
	"context"
)

func main() {
	var (
		config clientv3.Config
		client *clientv3.Client
		err error
		lease clientv3.Lease
		leaseGrantResp *clientv3.LeaseGrantResponse
		leaseId clientv3.LeaseID
		keepRespChan <-chan *clientv3.LeaseKeepAliveResponse
		keepResp *clientv3.LeaseKeepAliveResponse
		ctx context.Context
		cancelFunc context.CancelFunc
		kv clientv3.KV
		txn clientv3.Txn
		txnResp *clientv3.TxnResponse
	)

	// 客户端配置
	config = clientv3.Config{
		Endpoints: []string{"36.111.184.221:2379"},
		DialTimeout: 5 * time.Second,
	}

	// 建立连
    
func main() {
	var (
		config clientv3.Config
		client *clientv3.Client
		err error
		lease clientv3.Lease
		leaseGrantResp *clientv3.LeaseGrantResponse
		leaseId clientv3.LeaseID
		keepRespChan <-chan *clientv3.LeaseKeepAliveResponse
		keepResp *clientv3.LeaseKeepAliveResponse
		ctx context.Context
		cancelFunc context.CancelFunc
		kv clientv3.KV
		txn clientv3.Txn
		txnResp *clientv3.TxnResponse
	)

	// 客户端配置
	config = clientv3.Config{
		Endpoints: []string{"36.111.184.221:2379"},
		DialTimeout: 5 * time.Second,
	}

	// 建立连接
	if client, err = clientv3.New(config); err != nil {
		fmt.Println(err)
		return
	}

	// lease实现锁自动过期:
	// op操作
	// txn事务: if else then

	// 1, 上锁 (创建租约, 自动续租, 拿着租约去抢占一个key)
	lease = clientv3.NewLease(client)

	// 申请一个5秒的租约
	if leaseGrantResp, err = lease.Grant(context.TODO(), 5); err != nil {
		fmt.Println(err)
		return
	}

	// 拿到租约的ID
	leaseId = leaseGrantResp.ID

	// 准备一个用于取消自动续租的context
	ctx, cancelFunc = context.WithCancel(context.TODO())

	// 确保函数退出后, 自动续租会停止
	defer cancelFunc()
	defer lease.Revoke(context.TODO(), leaseId)

	// 5秒后会取消自动续租
	if keepRespChan, err = lease.KeepAlive(ctx, leaseId); err != nil {
		fmt.Println(err)
		return
	}

	// 处理续约应答的协程
	go func() {
		for {
			select {
			case keepResp = <- keepRespChan:
				if keepRespChan == nil {
					fmt.Println("租约已经失效了")
					goto END
				} else {	// 每秒会续租一次, 所以就会受到一次应答
					fmt.Println("收到自动续租应答:", keepResp.ID)
				}
			}
		}
	END:
	}()

	//  if 不存在key， then 设置它, else 抢锁失败
	kv = clientv3.NewKV(client)

	// 创建事务
	txn = kv.Txn(context.TODO())

	// 定义事务

	// 如果key不存在
	txn.If(clientv3.Compare(clientv3.CreateRevision("/cron/lock/job9"), "=", 0)).
		Then(clientv3.OpPut("/cron/lock/job9", "xxx", clientv3.WithLease(leaseId))).
		Else(clientv3.OpGet("/cron/lock/job9")) // 否则抢锁失败

	// 提交事务
	if txnResp, err = txn.Commit(); err != nil {
		fmt.Println(err)
		return // 没有问题
	}

	// 判断是否抢到了锁
	if !txnResp.Succeeded {
		fmt.Println("锁被占用:", string(txnResp.Responses[0].GetResponseRange().Kvs[0].Value))
		return
	}

	// 2, 处理业务

	fmt.Println("处理任务")
	time.Sleep(5 * time.Second)

	// 3, 释放锁(取消自动续租, 释放租约)
	// defer 会把租约释放掉, 关联的KV就被删除了
}