目录监控fsnotify包测试问题

下边测试的例子中，有文件变化时，case event := <-Watch.Events会触发三次，有用过的朋友能解释一下啊

package main

import (
    "flag"
    "log"
    "os/exec"
    "strings"
    "time"
    //    "sync"
    //    "time"

    "github.com/fsnotify/fsnotify"
)

var (
    sleeptime int
    path      string
    cmd       string
    args      []string
)

func init() {
    flag.IntVar(&sleeptime, "t", 30, "-t=30")
    flag.StringVar(&path, "p", "./", "-p=filepath or dirpath")
    flag.StringVar(&cmd, "c", "", "-c=command")
    str := flag.String("a", "", `-a="args1 args2"`)
    flag.Parse()
    args = strings.Split(*str, " ")
}

func main() {
    Watch, err := fsnotify.NewWatcher()
    if err != nil {
        log.Println("Init monitor error: ", err.Error())
        return
    }
    if err := Watch.Add(path); err != nil {
        log.Println("Add monitor path error: ", path)
        return
    }
    var (
    //        cron bool = false
    //        lock      = new(sync.Mutex)
    )
    for {
        select {
        case event := <-Watch.Events:
            if event.Op&fsnotify.Write == fsnotify.Write {
                log.Printf("Monitor event %s", event.String())
            }

            //            if !cron {
            //                cron = true
            //                go func() {
            //                    T := time.After(time.Second * time.Duration(sleeptime))
            //                    <-T
            //                    if err := call(cmd, args...); err != nil {
            //                        log.Println(err)
            //                    }
            //                    lock.Lock()
            //                    cron = false
            //                    lock.Unlock()
            //                }()
            //            }
        case err := <-Watch.Errors:
            log.Println(err)
            return
        }
    }
}

func call(programe string, args ...string) error {
    cmd := exec.Command(programe, args...)
    buf, err := cmd.Output()
    if err != nil {
        return err
    }
    log.Printf("\n%s\n", string(buf))
    return nil
}