Why is my thread still alive and how do I terminate it?

Question

So I previously had the same problem but I somehow fixed it. Now that I have started using Tkinter to display my output(Previously I just used the terminal) I have run into it again. I tried replicating my solution but it wont work. one of my threads(th1) wont terminate.

def wait_th2():
    while(True):
        if(not th2.is_alive()):
            print("1")
            time.sleep(5)
            root.destroy()
            break
        else:
            pass
    return

def start_process():
    global th2
    global th1
    th1 = Thread(target= wait_th2)
    th2 = Thread(target=main1)
    th2.start()
    return 

def on_closing():
    if messagebox.askokcancel("Quit", "Do you want to quit?"):
        qu_main.put('q') # this is to inform the th2 thread that the user wants to terminate the Script
        print("added q")
        th1.start()

if __name__ == '__main__':
    
    qu_main = qu()
    root = tk.Tk()
    root.title("Ping Script GUI")

    text_output = tk.Text(root, wrap=tk.WORD)
    text_output.pack(fill=tk.BOTH, expand=True)

    sys.stdout.write = redirect_print  # Redirect print statements to GUI

    start_process()

    root.protocol("WM_DELETE_WINDOW", on_closing)
    
    root.mainloop()

So I have a script that runs and gives me an output once the output is given it goes to sleep for a certain amount of time. I wanted the ability to terminate the script at any point of time so even if was sleeping. Where I ran into problem is when I try to terminate the script while It is still running. I want my Tkinter window to stay open till the script terminates and all the output is given so I started a new thread that checks if the previous thread is terminated or not and if not it keeps the Tkinter window open till the previous thread terminates.

If I use join all my windows freeze and the kernel crashes. If I use sys.exit() th1 thread still remains active. Now the reason I am not using ctrl+C is I want to convert this python code into an executable file and run it on my PC.

---

EDIT I now use Timer as a way to check if my thread as been terminate or not

def start_process():
    global th2,th1
    th1 = Timer(5, wait_th2)
    th2 = Thread(target=main1)
    th2.start()
    return 

def wait_th2():
    if(not th2.is_alive()):
        root.destroy()
        th1.cancel()
    else:
        th1 = Timer(5, wait_th2)
        th1.start()

But for some reason the kernel still crashes while trying to re-execute the code

Cannot execute code, session has been disposed. Please try restarting the Kernel. StdErr from Kernel Process Tcl_AsyncDelete: async handler deleted by the wrong thread