互斥锁

• 互斥锁的是控制共享资源进行访问的主要手段，目的是来保证在同一时刻只有一个线程对该对象进行访问。类似于开箱关箱子
  image.png

• golang中提供了一个sync.Mutex类型，并提供了一个Lock和UnLock方法，含义于图中相似。

下面是测试互斥锁的使用

package main

import (
    "fmt"
    "sync"
    "time"
)

var m *sync.Mutex
var goruntimeWaitGroup sync.WaitGroup

func main() {
    m = new(sync.Mutex)
    goruntimeWaitGroup.Add(1)
    go Worker(1, 5)
    goruntimeWaitGroup.Add(1)
    go Worker(2, 1)
    goruntimeWaitGroup.Add(1)
    go Worker(3, 1)
    goruntimeWaitGroup.Add(1)
    go Worker(4, 1)
    goruntimeWaitGroup.Add(1)
    go Worker(5, 3)
    goruntimeWaitGroup.Wait()
    fmt.Println("main Exit")
}

func Worker(i int, workerTime time.Duration) {
    defer goruntimeWaitGroup.Done()
    fmt.Println(i, "worker start")
    fmt.Println(i, "worker in lock")
    m.Lock()
    defer fmt.Println(i, "unlock")
    defer m.Unlock()
    fmt.Println("worker runing")
    time.Sleep(workerTime * time.Second)
}

运行结果：

4 worker start
4 worker in lock
worker runing
2 worker start
2 worker in lock
5 worker start
5 worker in lock
1 worker start
1 worker in lock
3 worker start
3 worker in lock
4 unlock
worker runing
2 unlock
worker runing
5 unlock
worker runing
1 unlock
worker runing
3 unlock
main Exit

解读：

• 互斥锁需成对出现，可以运用defer防止中间return，忘记写unclock造成死锁。
• 可以验证互斥锁的作用会保护共享资源，使同一时刻只有一个对象访问。