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关于etcd:etcd实现分布式锁

jiezi

转载自：etcd 实现分布式锁

当并发的访问共享资源的时候，如果没有加锁的话，无奈保障共享资源安全性和正确性。这个时候就须要用到锁

1、须要具备的个性

  1. 须要保障互斥拜访（分布式环境须要保障不同节点、不同线程的互斥拜访）
  2. 须要有超时机制，避免锁意外未开释，其余节点无奈获取到锁；也要保障工作可能失常执行实现，不能超时了工作还没完结，导致工作执行个别被开释锁
  3. 须要有阻塞和非阻塞两种申请锁的接口

2、本地锁

当业务执行在同一个线程内，也就是我初始化一个本地锁，其余申请也认这把锁。个别是服务部署在单机环境下。

咱们能够看下上面的例子，开 1000 个 goroutine 并发的给 Counter 做自增操作，后果会是什么样的呢？

package main

import (
    "fmt"
    "sync"
)

var sg sync.WaitGroup

type Counter struct {count int}

// 自增操作
func (m *Counter) Incr() {m.count++}

// 获取总数
func (m *Counter) Count() int {return m.count}

func main() {c := &Counter{}
    for i := 0; i < 1000; i++ {sg.Add(1)
    // 模仿并发申请
        go func() {c.Incr()
            sg.Done()}()}
    sg.Wait()

    fmt.Println(c.Count())
}

后果是 count 的数量并不是料想中的 1000，而是上面这样，每次打印出的后果都不一样，然而靠近 1000

user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
953
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
982
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
984

呈现这个问题的起因就是没有给自增操作加锁

上面咱们批改代码如下，在 Incr 中加上 go 的 mutex 互斥锁

package main

import (
    "fmt"
    "sync"
)

var sg sync.WaitGroup

type Counter struct {
    count int
    mu    sync.Mutex
}

func (m *Counter) Incr() {
  // 每次写之前先加锁，写完之后开释锁
    m.mu.Lock()
    defer m.mu.Unlock()
    m.count++
}

func (m *Counter) Count() int {return m.count}

func main() {c := &Counter{}
    for i := 0; i < 1000; i++ {sg.Add(1)
        go func() {c.Incr()
            sg.Done()}()}
    sg.Wait()

    fmt.Println(c.Count())
}

能够看到当初 count 失常输入 1000 了

user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
1000
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
1000
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
1000

3、etcd 分布式锁

简略部署一个 etcd 集群

├── docker-compose.yml
├── etcd
│   └── Dockerfile

Dockerfile 文件内容

FROM bitnami/etcd:latest

LABEL maintainer="liuyuede123 <liufutianoppo@163.com>"

Docker-compose.yml 内容

version: '3.5'
# 网络配置
networks:
  backend:
    driver: bridge

# 服务容器配置
services:
  etcd1:                                  # 自定义容器名称
    build:
      context: etcd                    # 指定构建应用的 Dockerfile 文件
    environment:
      - TZ=Asia/Shanghai
      - ALLOW_NONE_AUTHENTICATION=yes
      - ETCD_NAME=etcd1
      - ETCD_INITIAL_ADVERTISE_PEER_URLS=http://etcd1:2380
      - ETCD_LISTEN_PEER_URLS=http://0.0.0.0:2380
      - ETCD_LISTEN_CLIENT_URLS=http://0.0.0.0:2379
      - ETCD_ADVERTISE_CLIENT_URLS=http://etcd1:2379
      - ETCD_INITIAL_CLUSTER_TOKEN=etcd-cluster
      - ETCD_INITIAL_CLUSTER=etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380
      - ETCD_INITIAL_CLUSTER_STATE=new
    ports:                               # 设置端口映射
      - "12379:2379"
      - "12380:2380"
    networks:
      - backend
    restart: always

  etcd2: # 自定义容器名称
    build:
      context: etcd                    # 指定构建应用的 Dockerfile 文件
    environment:
      - TZ=Asia/Shanghai
      - ALLOW_NONE_AUTHENTICATION=yes
      - ETCD_NAME=etcd2
      - ETCD_INITIAL_ADVERTISE_PEER_URLS=http://etcd2:2380
      - ETCD_LISTEN_PEER_URLS=http://0.0.0.0:2380
      - ETCD_LISTEN_CLIENT_URLS=http://0.0.0.0:2379
      - ETCD_ADVERTISE_CLIENT_URLS=http://etcd2:2379
      - ETCD_INITIAL_CLUSTER_TOKEN=etcd-cluster
      - ETCD_INITIAL_CLUSTER=etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380
      - ETCD_INITIAL_CLUSTER_STATE=new
    ports: # 设置端口映射
      - "22379:2379"
      - "22380:2380"
    networks:
      - backend
    restart: always

  etcd3: # 自定义容器名称
    build:
      context: etcd                    # 指定构建应用的 Dockerfile 文件
    environment:
      - TZ=Asia/Shanghai
      - ALLOW_NONE_AUTHENTICATION=yes
      - ETCD_NAME=etcd3
      - ETCD_INITIAL_ADVERTISE_PEER_URLS=http://etcd3:2380
      - ETCD_LISTEN_PEER_URLS=http://0.0.0.0:2380
      - ETCD_LISTEN_CLIENT_URLS=http://0.0.0.0:2379
      - ETCD_ADVERTISE_CLIENT_URLS=http://etcd3:2379
      - ETCD_INITIAL_CLUSTER_TOKEN=etcd-cluster
      - ETCD_INITIAL_CLUSTER=etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380
      - ETCD_INITIAL_CLUSTER_STATE=new
    ports: # 设置端口映射
      - "32379:2379"
      - "32380:2380"
    networks:
      - backend
    restart: always

执行 docker-compose up -d 启动 etcd 服务，能够看到 docker 中曾经启动了 3 个服务

实现互斥拜访

package main

import (
    "fmt"
    clientv3 "go.etcd.io/etcd/client/v3"
    "go.etcd.io/etcd/client/v3/concurrency"
    "sync"
)

var sg sync.WaitGroup

type Counter struct {count int}

func (m *Counter) Incr() {m.count++}

func (m *Counter) Count() int {return m.count}

func main() {endpoints := []string{"http://127.0.0.1:12379", "http://127.0.0.1:22379", "http://127.0.0.1:32379"}
  // 初始化 etcd 客户端
    client, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
    if err != nil {fmt.Println(err)
        return
    }
    defer client.Close()

    counter := &Counter{}

    sg.Add(100)
    for i := 0; i < 100; i++ {go func() {
      // 这里会生成租约，默认是 60 秒
            session, err := concurrency.NewSession(client)
            if err != nil {panic(err)
            }
            defer session.Close()

            locker := concurrency.NewLocker(session, "/my-test-lock")
            locker.Lock()
            counter.Incr()
            locker.Unlock()
            sg.Done()}()}
    sg.Wait()

    fmt.Println("count:", counter.Count())
}

执行后果：

user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
count: 100
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
count: 100
 user@userdeMacBook-Pro  ~/go/src/go-demo/mutex  go run main.go
count: 100

实现超时机制

当某个客户端持有锁时，因为某些起因导致锁未开释，就会导致这个客户端始终持有这把锁，其余客户端始终获取不到锁。所以须要分布式锁实现超时机制，当锁未开释时，会因为 etcd 的租约会到期而开释锁。当业务失常解决时，租约到期之前会持续续约，晓得业务处理完毕开释锁。

package main

import (
    "fmt"
    clientv3 "go.etcd.io/etcd/client/v3"
    "go.etcd.io/etcd/client/v3/concurrency"
    "sync"
    "time"
)

var sg sync.WaitGroup

type Counter struct {count int}

func (m *Counter) Incr() {m.count++}

func (m *Counter) Count() int {return m.count}

func main() {endpoints := []string{"http://127.0.0.1:12379", "http://127.0.0.1:22379", "http://127.0.0.1:32379"}
    client, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
    if err != nil {fmt.Println(err)
        return
    }
    defer client.Close()

    counter := &Counter{}

    session, err := concurrency.NewSession(client)
    if err != nil {panic(err)
    }
    defer session.Close()

    locker := concurrency.NewLocker(session, "/my-test-lock")
    fmt.Println("locking...", time.Now().Format("2006-01-02 15:04:05"))
    locker.Lock()
    fmt.Println("locked...", time.Now().Format("2006-01-02 15:04:05"))
  // 模仿业务
    time.Sleep(100 * time.Second)
    counter.Incr()
    locker.Unlock()
    fmt.Println("released...", time.Now().Format("2006-01-02 15:04:05"))

    fmt.Println("count:", counter.Count())
}

命令行开 2 个窗口，第一个窗口执行程序并获取锁，之后模仿意外退出并没有调用 unlock 办法

go run main.go
locking... 2022-09-03 23:41:48 # 租约生成工夫
locked... 2022-09-03 23:41:48
^Csignal: interrupt

第二个窗口，在第一个窗口退出之前尝试获取锁，此时是阻塞状态。第一个窗口退出之后因为租约还没到期，第二个窗口还是获取锁的状态。等到第一个窗口租约到期（默认 60 秒），第二个获取锁胜利

locking... 2022-09-03 23:41:52
locked... 2022-09-03 23:42:48 # 第一个租约 60 秒到期，获取锁胜利
released... 2022-09-03 23:44:28
count: 1

实现阻塞和非阻塞接口

下面的例子中曾经实现了阻塞接口，即以后有获取到锁的申请，则其余申请阻塞期待锁开释

非阻塞的形式就是尝试获取锁，如果失败立刻返回。etcd 中是实现了 tryLock 办法

// TryLock locks the mutex if not already locked by another session.
// If lock is held by another session, return immediately after attempting necessary cleanup
// The ctx argument is used for the sending/receiving Txn RPC.
func (m *Mutex) TryLock(ctx context.Context) error {

具体看上面的例子

package main

import (
    "context"
    "fmt"
    clientv3 "go.etcd.io/etcd/client/v3"
    "go.etcd.io/etcd/client/v3/concurrency"
    "sync"
    "time"
)

var sg sync.WaitGroup

type Counter struct {count int}

func (m *Counter) Incr() {m.count++}

func (m *Counter) Count() int {return m.count}

func main() {endpoints := []string{"http://127.0.0.1:12379", "http://127.0.0.1:22379", "http://127.0.0.1:32379"}
    client, err := clientv3.New(clientv3.Config{Endpoints: endpoints})
    if err != nil {fmt.Println(err)
        return
    }
    defer client.Close()

    counter := &Counter{}

    session, err := concurrency.NewSession(client)
    if err != nil {panic(err)
    }
    defer session.Close()

  // 此处应用 newMutex 初始化
    locker := concurrency.NewMutex(session, "/my-test-lock")
    fmt.Println("locking...", time.Now().Format("2006-01-02 15:04:05"))
    err = locker.TryLock(context.Background())
  // 获取锁失败就抛错
    if err != nil {fmt.Println("lock failed", err)
        return
    }
    fmt.Println("locked...", time.Now().Format("2006-01-02 15:04:05"))
    time.Sleep(100 * time.Second)
    counter.Incr()
    err = locker.Unlock(context.Background())
    if err != nil {fmt.Println("unlock failed", err)
        return
    }
    fmt.Println("released...", time.Now().Format("2006-01-02 15:04:05"))

    fmt.Println("count:", counter.Count())
}

窗口 1、窗口 2 执行后果

go run main.go
locking... 2022-09-04 00:00:21
locked... 2022-09-04 00:00:21
released... 2022-09-04 00:02:01
count: 1
go run main.go
locking... 2022-09-04 00:00:27
lock failed mutex: Locked by another session
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