How to control parallel processes with condition

Question

I want to control my processes while I not found working url.

But I have NameError: name 'status' is not defined due to threads not waiting to declare a variable

import requests
from multiprocessing import Process


def first_function(i):
    global status
    status = False
    try:
        response = requests.get(f'https://ru.hexlet.io/{i}')
        if response.status_code == 200:
            status = True
    except Exception as e:
        print(str(e))


def second_function():
    for i in [1,2,3,4,5,6,'courses',8,9,10]:
        Process(target=first_function, args=(i, )).start()
        print(i)
        if status:
            print('working', i)
            break


if __name__ == '__main__':
    second_function()

Answer 1

I suggest using a multiprocessing.pool.Pool to limit the number of processes that are run concurrently (since you have indicated there might be a very large number of them).

If you use its apply_async() method to "submit" tasks to it, you can use the optional callback argumet to specify a function that will get called whenever one of the subprocesses finishes. This provides a way to terminate further processing by other processes submitted to the pool .

import multiprocessing as mp
import requests


def worker(i):
    try:
        response = requests.get(f'https://ru.hexlet.io/{i}')
        if response.status_code == 200:
            return i
    except Exception as exc:
        print(f'{i!r} caused {exc}')
    return None


if __name__ == '__main__':

    def notify(i):
        """Called when a Pool worker process finishes execution."""
        if i is not None:
            print(f'{i!r} worked')
            pool.terminate()  # Stops worker processes immediately.

    pool = mp.Pool()

    for i in [1,2,3,4,5,6,'courses',8,9,10]:
        pool.apply_async(worker, (i,), callback=notify)

    pool.close()
    pool.join()
    print('fini')

Output:

'courses' worked
fini