西洋汇golang面试题代码，我感觉写的功能还算完整，但还是没得到面试机会

package main

import (
       "encoding/json"
       "fmt"
       "io/ioutil"
       "net/http"
       "os"
       "os/exec"
       "sync"
       "time"
)

type Task struct {
       Id       string   `json:"id"`
       Cmd      string   `json:"cmd,omitempty"`
       Args     []string `json:"args,omitempty"`
       Interval int      `json:"interval,omitempty"`
       stop     chan struct{}
}

func (task *Task) Start() {
       go func() {
       label:
              for {
                     select {
                     case <-time.After(time.Duration(task.Interval) * time.Millisecond):
                            cmd := exec.Command(task.Cmd, task.Args...)
                            cmd.Stdout = os.Stdout
                            cmd.Run()
                     case <-task.stop:
                            break label
                     }
              }
       }()
}

func (task *Task) Stop() {
       task.stop <- struct{}{}
}

type Response struct {
       Ok    bool   `json:"ok"`
       Id    string `json:"id,omitempty"`
       Error string `json:"error,omitempty"`
}

var cron Cron

type Cron struct {
       mutex sync.Mutex
       jobs  map[string]*Task
}

func cronManager(w http.ResponseWriter, req *http.Request) {
       defer req.Body.Close()
       var task Task
       cont, _ := ioutil.ReadAll(req.Body)
       json.Unmarshal(cont, &task)
       reqTaskId := task.Id

       cron.mutex.Lock()
       defer cron.mutex.Unlock()
       if req.Method == "POST" {
              if _, ok := cron.jobs[reqTaskId]; ok {
                     response := Response{
                            Ok: false, Error: "The task " + reqTaskId + " already exists.",
                     }
                     cont, _ = json.Marshal(response)
                     w.WriteHeader(409)
                     w.Write(cont)
              } else {
                     task.stop = make(chan struct{})
                     cron.jobs[task.Id] = &task
                     task.Start()
                     response := Response{
                            Ok: true, Id: task.Id,
                     }
                     cont, _ = json.Marshal(response)
                     w.WriteHeader(200)
                     w.Write(cont)
              }
       }

       if req.Method == "DELETE" {
              if task, ok := cron.jobs[task.Id]; ok {
                     delete(cron.jobs, task.Id)
                     task.Stop()
                     response := Response{Ok: true, Id: task.Id}
                     cont, _ = json.Marshal(response)
                     w.WriteHeader(200)
                     w.Write(cont)
              } else {
                     response := Response{
                            Ok: false, Error: "The task " + reqTaskId + " is not found.",
                     }
                     cont, _ = json.Marshal(response)
                     w.WriteHeader(404)
                     w.Write(cont)
              }
       }
}

func main() {
       if len(os.Args) != 2 {
              fmt.Println("usage: ./gocron port")
              return
       }
       fmt.Println("GoCron listening on 4567")
       cron.jobs = make(map[string]*Task)
       http.HandleFunc("/", cronManager)
       http.ListenAndServe(":"+os.Args[1], nil)
}