【golang】sync包once 只执行一次代码

once 只执行一次代码，竞争条件下也是安全的；

func main() {
  var once = Once {
    func() {
      fmt.Println("Only once")
    },
    0,
    sync.Mutex{},
  }
  
  goroutine(&once)
  goroutine(&once)
 
  time.Sleep(1) // wait for goroutines to complete
}func goroutine(once *Once) {
  once.Do()
}