Mutex
用途: 排它锁, 有锁定和未锁定状态， 当处于锁定状态时， 其它尝试进行的锁定操作都被等待，直到解锁

package main
import (
    "fmt"
    "sync"
    "time"
)

var m *sync.Mutex

func main() {
     m = new(sync.Mutex)
    go lock(1)
       time.Sleep(time.Second)
    lock(2)
    fmt.Printf("%s\n", "exit!")
}

func lock(i int) {
    println(i, "lock start")
    m.Lock()
    println(i, "lock")
    time.Sleep(10 * time.Second)
    m.Unlock()
    println(i, "unlock")
}