go 并发编程

package main

import (
    "fmt"
    "time"
)

func say(s string) {
    for i := 0; i < 4; i++ {
        time.Sleep(100 * time.Millisecond)
        fmt.Println(s, i)
    }
}
func main() {
    go say("hello")
    say("world")
}