collbacks_with_threads.py

import time
import threading


def set_timeout(delay, callback):
    def target():
        time.sleep(delay)
        callback()
    threading.Thread(target=target).start()


if __name__ == '__main__':
    set_timeout(1, lambda: print(1))
    set_timeout(10, lambda: print(10))
    set_timeout(5, lambda: print(5))
    set_timeout(3, lambda: print(3))
    set_timeout(1, lambda: print(1))
    set_timeout(2, lambda: print(2))
    set_timeout(7, lambda: print(7))
    set_timeout(4, lambda: print(4))

eventloop_callbacks_no_threads.py

import time
from queue import Queue


def _make_infinity_queue():
    return Queue(maxsize=-1)


_queue = _make_infinity_queue()


def set_timeout(delay, callback):
    start_time = time.time()

    def wrapper():
        if time.time() >= start_time + delay:
            _queue.put(callback)
        else:
            _queue.put(wrapper)

    _queue.put(wrapper)


class EventLoop:
    def __init__(self, initial_target):
        _queue.put(initial_target)

    # noinspection PyMethodMayBeStatic
    def run(self):
        while not _queue.empty():
            func = _queue.get()
            func()


if __name__ == '__main__':
    def async_fun():
        set_timeout(1, lambda: print(1))
        set_timeout(10, lambda: print(10))
        set_timeout(5, lambda: print(5))
        set_timeout(3, lambda: print(3))
        set_timeout(1, lambda: print(1))
        set_timeout(2, lambda: print(2))
        set_timeout(7, lambda: print(7))
        set_timeout(4, lambda: print(4))
        print("exiting from `async_fun`")
    EventLoop(async_fun).run()

eventloop_callbacks_with_threads.py

import time
from multiprocessing.pool import ThreadPool
from queue import Queue


def _make_infinity_queue():
    return Queue(maxsize=-1)


_thread_pool = ThreadPool(processes=1)
_queue = _make_infinity_queue()


def set_timeout(delay, callback):
    start_time = time.time()

    def wrapper():
        if time.time() >= start_time + delay:
            _queue.put(callback)
        else:
            _queue.put(wrapper)

    _queue.put(wrapper)


class EventLoop:
    def __init__(self, initial_target):
        _queue.put(initial_target)

    # noinspection PyMethodMayBeStatic
    def run(self):
        while True:
            target = _queue.get()
            _thread_pool.apply(target)


if __name__ == '__main__':
    def async_fun():
        set_timeout(1, lambda: print(1))
        set_timeout(10, lambda: print(10))
        set_timeout(5, lambda: print(5))
        set_timeout(3, lambda: print(3))
        set_timeout(1, lambda: print(1))
        set_timeout(2, lambda: print(2))
        set_timeout(7, lambda: print(7))
        set_timeout(4, lambda: print(4))
        print("exiting from `async_fun`")
    EventLoop(async_fun).run()

synchronous_callbacks.py

import time


def set_timeout(delay, callback):
    time.sleep(delay)
    callback()


if __name__ == '__main__':
    set_timeout(1, lambda: print(1))
    set_timeout(10, lambda: print(10))
    set_timeout(5, lambda: print(5))
    set_timeout(3, lambda: print(3))
    set_timeout(1, lambda: print(1))
    set_timeout(2, lambda: print(2))
    set_timeout(7, lambda: print(7))
    set_timeout(4, lambda: print(4))