Понимание потоков в python/tkinter и matplotlib. Объясните пожалуйста где ошибка?

import random
import threading
import time
import tkinter as tk
from queue import Empty, Queue
from time import time as timer
from matplotlib.figure import Figure
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg


def get_xy_from_db(id):  # generate dummy data
    #time.sleep(random.random())  # emulate blocking function
    list_x = list(range(1, 16))
    list_y = list(random.sample(range(0,100),15))
    res_lst = list_x + list_y
    return res_lst


def poll_db(id, emit):  # NOTE: interval is independant from the delay
    while True:
        #time.sleep(interval)
        emit(get_xy_from_db(id))


def poll_db_2(id, emit):  # NOTE: interval is independant from the delay
    while True:
        #time.sleep(interval)
        emit(get_xy_from_db(id))


def make_x_y(list_a):    
    done_x=list_a[:15]
    done_y=list_a[15:]    
    return done_x, done_y    


def start_polling_loop(root, q, delay):
    def loop():
        timeout_millis = round(delay - (1000 * timer()) % delay)
        root.after(timeout_millis, loop)
        a.clear()
        try:
            data = q.get(block=False)
            x, y = make_x_y(data)
            a.plot(x, y)
            canvas.draw()
        except Empty:
            return

    root.after_idle(loop)  # start


def start_polling_loop_2(root, q_2, delay):
    def loop():
        timeout_millis = round(delay - (1000 * timer()) % delay)
        root.after(timeout_millis, loop)
        a1.clear()
        try:
            data = q_2.get(block=False)
            x, y = make_x_y(data)
            a1.plot(x, y)
            canvas.draw()
        except Empty:
            return

    root.after_idle(loop)  # start

if __name__ == "__main__":
    root = tk.Tk()
    q = Queue()  # первая очередь для первого графика
    q_2 = Queue()  # вторая очередь для второго

    # соответствующие потоки
    threading.Thread(target=poll_db, args=[1, q.put], daemon=True).start()
    threading.Thread(target=poll_db_2, args=[2, q_2.put], daemon=True).start()

    start_polling_loop(root, q, delay=40)
    start_polling_loop_2(root, q_2, delay=40)

    f = Figure(figsize=(8, 4), dpi=100)

    a = f.add_subplot(1, 2, 1)  # расширим сетку для второго графика
    a1 = f.add_subplot(1, 2, 2)  # добавим второй график в сетку

    canvas = FigureCanvasTkAgg(f, master=root)
    canvas.show()
    canvas.get_tk_widget().grid(row=0, column=0)

    root.mainloop()