//go func 和主线程之间的关系是并行和竞争关系

package main

import (

    "fmt"

    "sync"

    "time"

)

var l sync.Mutex

var m *sync.Mutex

func main() {

    m = new(sync.Mutex)

    go lock()

    time.Sleep( * time.Second)

    fmt.Printf("%s\n", "exit!")

}

func lock(i int) {

    println(i, "lock start")

    m.Lock()

    println(i, "lock")

    time.Sleep( * time.Second)

    m.Unlock()

    println(i, "unlock")

}