tkinter after() 方法双线程运行启停生成随机数

import time
import tkinter as tk
import random

window = tk.Tk()

var1 = tk.StringVar()
text = tk.Label(window, textvariable=var1)
text.grid(row=0, column=1)

going = True
is_run = False


def getnum(var1):
    global going
    a = random.randint(0, 100000)
    str_a=str(a)
    var1.set(str_a)
    if going:
        window.after(100, getnum, var1)
    else:
        going = True
        return


def start(var1):
    global is_run
    if is_run:
        return
    is_run = True
    getnum(var1)


def stop():
    global going, is_run
    if is_run:
        going = False
        is_run = False


but = tk.Button(window, text="开始", command=lambda: start(var1))
but.grid(row=1, column=1)
but2 = tk.Button(window, text="结束", command=stop)
but2.grid(row=1, column=2)

window.mainloop()