#!/usr/bin/env python3

import os
import threading

def a():
    def printer_thread():
        n = 0
        while n < NUM_PRINTS:
            print(f"Hello from thread (loop {n})")
            n += 1
        print(f"Thread dying happy")
    t = threading.Thread(target=printer_thread)
    t.start()
    # same effect happens if we start the thread using
    # _thread.start_new_thread, or threading.Thread,
    # or a ThreadPoolExecutor.

def b():
    pids = []
    for n in range(NUM_FORKS):
        if pid := os.fork():
            pids.append(pid)
        else:
            if LETS_CAUSE_A_DEADLOCK:
                print(f"Hello from process {n}")
            os._exit(0)
    for pid in pids:
        wpid, wsts = os.waitpid(pid, 0)
    # same effect happens if we start the process using
    # os.fork, or mp.Process, or a ProcessPoolExecutor.

if __name__ == "__main__":

    NUM_FORKS = NUM_PRINTS = 500

    # The deadlock occurs if and only if the child prints
    LETS_CAUSE_A_DEADLOCK = True

    # The user calls some function, unaware that it uses threads.
    a()

    # The user calls another function, unaware that it forks.
    b()

    print(f"Main dying happy")