这篇文章给大家介绍etcd租约机制及自动过期的实例分析，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
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对于实现分布式乐观锁非常重要。如果锁了，突然宕机了，锁是需要自动释放的。所以这锁在etcd里是需要生命期的。
过期演示：
package main
import (
"context"
"fmt"
"go.etcd.io/etcd/clientv3"
"time"
)
func main() {
var (
config clientv3.Config
client *clientv3.Client
err error
lease clientv3.Lease
leaseGrantResp *clientv3.LeaseGrantResponse
leaseId clientv3.LeaseID
putResp *clientv3.PutResponse
kv clientv3.KV
getResp *clientv3.GetResponse
)
//客户端配置
config = clientv3.Config{
Endpoints: []string{"0.0.0.0:2379"}, //集群列表
DialTimeout: 5 * time.Second,
}
//建立客户端
if client, err = clientv3.New(config); err != nil {
fmt.Println(err)
return
}
//申请一个lease(租约)
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
//获得kv api子集
kv = clientv3.NewKV(client)
//put一个kv，让它与租约关联起来，从而实现10秒后自动过期
if putResp, err = kv.Put(context.TODO(), "/cron/lock/job1", "", clientv3.WithLease(leaseId)); err != nil {
fmt.Println(err)
return
}
fmt.Println("写入成功:", putResp.Header.Revision)
//定时看key过期没
for {
if getResp, err = kv.Get(context.TODO(), "/cron/lock/job1"); err != nil {
fmt.Println(err)
return
}
if getResp.Count == 0 {
fmt.Println("kv过期了")
break
}
fmt.Println("还没过期:", getResp.Kvs)
time.Sleep(time.Second)
}
}[root@bogon etcd]# go run demo6.go
写入成功: 27
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
还没过期: [key:"/cron/lock/job1" create_revision:27 mod_revision:27 version:1 lease:7587837741646622005 ]
kv过期了
[root@bogon etcd]#
申请一把分布式锁的时候，是谁抢到了key就是抢到了锁，如果不主动释放这锁，按道理讲不应该让租约过期，租约过期主要是为了程序宕掉之后，锁自动释放，防止程序异常退出。如果程序抢到了这个锁，我们希望锁一直不失效，知道我们主动释放它：
package main
import (
"context"
"fmt"
"go.etcd.io/etcd/clientv3"
"time"
)
func main() {
var (
config clientv3.Config
client *clientv3.Client
err error
lease clientv3.Lease
leaseGrantResp *clientv3.LeaseGrantResponse
leaseId clientv3.LeaseID
putResp *clientv3.PutResponse
kv clientv3.KV
getResp *clientv3.GetResponse
keepResp *clientv3.LeaseKeepAliveResponse
keepRespChan <-chan *clientv3.LeaseKeepAliveResponse //只读channel
)
//客户端配置
config = clientv3.Config{
Endpoints: []string{"0.0.0.0:2379"}, //集群列表
DialTimeout: 5 * time.Second,
}
//建立客户端
if client, err = clientv3.New(config); err != nil {
fmt.Println(err)
return
}
//申请一个lease(租约)
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
//(自动续租)当我们申请了租约之后，我们就可以启动一个续租
if keepRespChan, err = lease.KeepAlive(context.TODO(), leaseId); err != nil {
fmt.Println(err)
return
}
//处理续租应答的协程
go func() {
for {
select {
case keepResp = <-keepRespChan:
if keepRespChan == nil {
fmt.Println("租约已经失效")
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:
}()
//获得kv api子集
kv = clientv3.NewKV(client)
//put一个kv，让它与租约关联起来，从而实现10秒后自动过期
if putResp, err = kv.Put(context.TODO(), "/cron/lock/job1", "", clientv3.WithLease(leaseId)); err != nil {
fmt.Println(err)
return
}
fmt.Println("写入成功:", putResp.Header.Revision)
//定时看key过期没
for {
if getResp, err = kv.Get(context.TODO(), "/cron/lock/job1"); err != nil {
fmt.Println(err)
return
}
if getResp.Count == 0 {
fmt.Println("kv过期了")
break
}
fmt.Println("还没过期:", getResp.Kvs)
time.Sleep(time.Second)
}
}[root@bogon etcd]# go run demo7.go
写入成功: 30
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
还没过期: [key:"/cron/lock/job1" create_revision:29 mod_revision:30 version:2 lease:7587837741646622039 ]
收到自动续租应答: 7587837741646622039
......
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