Python Google Sheets APIv4: Multiprocessing and Multithreading at the same time

Question

I can get multiprocessing and multithreading to work with google sheets APIv4 independently, but I can't get them to work together.

Multiprocessing (this works):

from multiprocessing import Pool
import threading
import pandas

class B:
    def __init__(self):
        self.core = 10
        self.b()

    def b(self):
        p = Pool(self.core)
        p.map(multicore, range(10))

def multicore(*args):
    thread = 0
    if thread == 1:
        thread_list = []
        for i in range(10):
            thread = threading.Thread(target=output_function, args=(i,))
            thread_list.append(thread)
            thread.start()
    else:
        output_function(*args)

def output_function(*args):
    x = args[0]

    print(x * x)
    g.build_service()

    g.export_df(g.test_API_key, ['output!A' + str(x + 1)], [pandas.DataFrame([[x * x]])], 'n')

Multithreading (this also works):

def just_threading():
    thread = 1
    if thread == 1:
        thread_list = []
        for i in range(10):
            thread = threading.Thread(target=output_function, args=(i,))
            thread_list.append(thread)
            thread.start()

def output_function(*args):
    x = args[0]

    print(x * x)
    g.build_service()

    g.export_df(g.test_API_key, ['output!A' + str(x + 1)], [pandas.DataFrame([[x * x]])], 'n')

But when I combine them by setting thread = 1 for the first example, I get absolutely no output to google sheets ( print(x*x) still works).

What's funny is that if I take away g.build_service() , it will output a few lines until it runs into Thread safety issues outlined here: https://developers.google.com/api-client-library/python/guide/thread_safety with error ssl.SSLError: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:2273) . So rebuilding the service does matter, but I see no output to sheets!

Answer 1

You need to wait for the threads to finish their work, otherwise the main thread will exit before they complete.

After you've launched the threads, run:

for t in thread_list:
    t.join()