GO语言临界资源安全问题的深入理解

package main
​
import (
    "fmt"
    "time"
)
​
func main()  {
    a := 1
    go func() {
        a = 2
        fmt.Println("子goroutine。。",a)
    }()
    a = 3
    time.Sleep(1)
    fmt.Println("main goroutine。。",a)
}

package main
​
import (
    "fmt"
    "math/rand"
    "time"
)
​
//全局变量
var ticket = 10 // 100张票
​
func main() {
    /*
    4个goroutine，模拟4个售票口，4个子程序操作同一个共享数据。
     */
    go saleTickets("售票口1") // g1,100
    go saleTickets("售票口2") // g2,100
    go saleTickets("售票口3") //g3,100
    go saleTickets("售票口4") //g4,100
​
    time.Sleep(5*time.Second)
}
​
func saleTickets(name string) {
    rand.Seed(time.Now().UnixNano())
    //for i:=1;i<=100;i++{
    //  fmt.Println(name,"售出：",i)
    //}
    for { //ticket=1
        if ticket > 0 { //g1,g3,g2,g4
            //睡眠
            time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
            // g1 ,g3, g2,g4
            fmt.Println(name, "售出：", ticket)  // 1 , 0, -1 , -2
            ticket--   //0 , -1 ,-2 , -3
        } else {
            fmt.Println(name,"售罄，没有票了。。")
            break
        }
    }
}
​

package main
​
import (
    "fmt"
    "math/rand"
    "time"
    "sync"
)
​
//全局变量
var ticket = 10 // 100张票
​
var wg sync.WaitGroup
var matex sync.Mutex // 创建锁头
​
func main() {
    /*
    4个goroutine，模拟4个售票口，4个子程序操作同一个共享数据。
     */
    wg.Add(4)
    go saleTickets("售票口1") // g1,100
    go saleTickets("售票口2") // g2,100
    go saleTickets("售票口3") //g3,100
    go saleTickets("售票口4") //g4,100
    wg.Wait()              // main要等待。。。
​
    //time.Sleep(5*time.Second)
}
​
func saleTickets(name string) {
    rand.Seed(time.Now().UnixNano())
    defer wg.Done()
    //for i:=1;i<=100;i++{
    //  fmt.Println(name,"售出：",i)
    //}
    for { //ticket=1
        matex.Lock()
        if ticket > 0 { //g1,g3,g2,g4
            //睡眠
            time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
            // g1 ,g3, g2,g4
            fmt.Println(name, "售出：", ticket) // 1 , 0, -1 , -2
            ticket--                         //0 , -1 ,-2 , -3
        } else {
            matex.Unlock() //解锁
            fmt.Println(name, "售罄，没有票了。。")
            break
        }
        matex.Unlock() //解锁
    }
}
​