监听端口号后修改代码，重新run 后，发现还是原来的程序，换端口后有效

package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", handler)
    http.HandleFunc("/hello", hello)
    http.ListenAndServe("localhost:8884", nil)

}
func handler(w http.ResponseWriter, req *http.Request) {
    req.ParseForm()
    if len(req.Form["name"]) > 0 {
        fmt.Fprint(w, "你好，", req.Form["name"][0])
    } else {
        fmt.Fprint(w, "hello")
    }
}

修改后go run ，只有改了端口号再访问修改的代码才会生效，原先的端口后全被占着，怎么破，大神求解！！！