Python kivy and multiprocessing bug - python-3.x

Question

I am stuck on writing a very simple kivy gui with 2 buttons.
button_1 launches the countdown in multiprocessing. It works.
button_2 is supposed to end the countdown in multiprocessing. That does not work...
Can anyone please point out what I am doing wrong and why?
Thank you kindly in advance.
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout
import multiprocessing
import time
class MyApp(App):
list_of_objects_in_class = []
def build(self):
layout = BoxLayout()
button_1 = Button(text='launch_countdown', on_press=self.launch_countdown)
button_2 = Button(text='end_the_countdown', on_press=self.end_the_countdown)
layout.add_widget(button_1)
layout.add_widget(button_2)
return layout
#staticmethod
def actual_countdown_function(*args):
print('I am launching the countdown!')
for count in range(5, 0, -1):
print(count)
time.sleep(1)
print('Countdown Finished!!!') # When I press end_the_countdown button, this is NOT supposed to be printed.
def launch_countdown(self, *args):
MyApp.list_of_objects_in_class.append(multiprocessing.Process(target=MyApp.actual_countdown_function, args=()))
MyApp.list_of_objects_in_class[0].start()
def end_the_countdown(self, *args):
print('I am terminating the countdown early!')
try:
MyApp.list_of_objects_in_class[0].terminate()
MyApp.list_of_objects_in_class.clear()
except:
pass
if __name__ == "__main__":
MyApp().run()
I tested to see if .terminate() works on my system, it works. The script below terminates successfully but the script above does NOT...
import multiprocessing
import time
def print_one():
time.sleep(3)
print('This does NOT get printed because proc.terminate() works on my Linux Mint OS')
def print_two():
print('This gets printed')
process_to_terminate = multiprocessing.Process(target=print_one, args=())
process_to_terminate.start()
process_to_keep_and_NOT_terminate = multiprocessing.Process(target=print_two, args=())
process_to_keep_and_NOT_terminate.start()
process_to_terminate.terminate() # Works and kills print_one function

Answer 1

It's better to use threads indeed to run such a small tasks.
Anyway, I think, the original problem could be solved by setting SIGTERM handler in a child process, because it seems to be ignoring SIGTERM by default:
def actual_countdown_function(self, *args):
+ signal.signal(signal.SIGTERM, lambda *_, **__: sys.exit(0))
print('I am launching the countdown!')
But, TBH, if you will really need a way to manage child process, I strongly recommend to use Locks/Conditions/Queues instead. They have almost the same API like all the threading primitives, but built to interact over pipes/shared-memory/sockets/etc.

Answer 2

after many different attempts, I was able to solve my own problem by using threading instead of multiprocessing.
Here is the code:
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.boxlayout import BoxLayout
import threading
import time
class MyApp(App):
my_var = True
list_of_objects_in_class = []
def build(self):
layout = BoxLayout(size =(300, 300))
button_1 = Button(text='launch_countdown', on_press=self.launch_countdown)
button_2 = Button(text='end_the_countdown', on_press=self.end_the_countdown, height = "100", width = 140)
layout.add_widget(button_1)
layout.add_widget(button_2)
return layout
def actual_countdown_function(self, *args):
print('I am launching the countdown!')
x = 5
while x != 0:
new_var = self.my_var
if new_var == False:
break
time.sleep(1)
print(x, new_var)
x -=1
del(new_var)
print('Countdown Finished!!!') # When I press end_the_countdown button, this is NOT supposed to be printed.
def launch_countdown(self, *args):
t1 = threading.Thread(target=self.actual_countdown_function)
t1.start()
def end_the_countdown(self, *args):
print('I am terminating the countdown early!')
self.my_var = not self.my_var
print(self.my_var)
self.list_of_objects_in_class.clear()
if __name__ == "__main__":
MyApp().run()