Как остановить вложенные вычисления и закрыть окно верхнего уровня в tkinter

Я внес несколько изменений, прежде всего добавил protocol для root и progress_window.

Я также создал флаг killed, который используется для разрыва циклов for. Я поместил их в функцию, вызываемую after.

Это останавливает TclError: Invalid command name .!toplevel.!label2

from tkinter import Tk, Toplevel, Button, Label, TOP, BOTH, DoubleVar
from tkinter.ttk import Progressbar
import time 

killed  =  False

root  =  Tk()
root.configure(bg = 'lightgray')
root.wm_title("Main")

root.update()

progress_window  =  Toplevel()

def stop():
    global killed
    killed = True
    progress_window.destroy()
    root.destroy()

# Added protocol controls for exit

root.protocol( "WM_DELETE_WINDOW", stop )
progress_window.protocol( "WM_DELETE_WINDOW", stop )

progress_window.attributes('-topmost', 'true')
progress_window.configure(bg = 'lightgrey')
progress_window.wm_title("Progress")
progress_window_label  =  Label(root, text = "")
progress_window.geometry('600x300')
progress_window_label.pack()

M = 4 # outer loop
N = 5 # inner loop

progress1_var = DoubleVar()
progress1bar = Progressbar(master = progress_window, variable = progress1_var, length = M)    
progress1bar.pack(side = TOP, ipady = 5, fill = BOTH, expand = True)
progress1_var.set(0)
progress1bar.update()
progress1bar_label = Label(master = progress_window, text = 'Bar1', bg = 'lightgray')
progress1bar_label.pack(side = TOP, pady = 5, fill = BOTH, expand = True)

progress2_var  =  DoubleVar()
progress2bar = Progressbar(master = progress_window, variable = progress2_var, length = N)
progress2bar.pack(side = TOP, ipady = 5, fill = BOTH, expand = True)

progress2_var.set(0)
progress2bar.update()

progress2bar_label = Label(master = progress_window, text = 'Bar2', bg = 'lightgray')
progress2bar_label.pack(side = TOP, pady = 5, fill = BOTH, expand = True)

def process():
    for t in range(M):
        if killed:
            break
        progress1_var.set(t/M)
        progress1bar_label.config(text = "Bar 1:    " + str( round( (t+1)/M*100, 3)) + "%")
        progress1bar.update()
        progress2_var.set(0)
        progress2bar.update()
        for i in range(N):
            progress2_var.set(i/N)
            time.sleep(1.0)
            if killed:
                break
            progress2bar_label.config(text = "Bar 2:    " + str( round( (i+1)/N*100, 3)) + "%")
            progress2bar.update()

stop_button = Button(master = progress_window, text = "Cancel", command = stop)
stop_button.pack(side = TOP, pady = 5, fill = BOTH, expand = True)

root.after( 1000, process )
root.mainloop()