Start a WSGI app with N number of processes with Bjoern.

start.py

"""
Starts a WSGI application with Bjoern; https://github.com/jonashaag/bjoern.

Make sure 'libev' is installed in your system.

Gist found here:
    https://gist.github.com/synchronizing/e60532664fd50bb17058f24e3b674276
"""

import logging
import multiprocessing
import os
import signal

import bjoern


def wsgi_application():
    """
    Retrieves WSGI application to start.
    """
    from django.core.wsgi import get_wsgi_application

    # Update line below if using Django.
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "djangosite.djangosite.settings")
    return get_wsgi_application()


def start(host: str, port: int, workers: int):
    """
    Starts the server with N workers.
    """

    # Initial logger for main process.
    logging.getLogger().setLevel(logging.INFO)
    logger = logging.getLogger(__name__)
    logger_handler = logging.StreamHandler()
    logger_handler.setLevel(logging.INFO)
    logger_handler.setFormatter(logging.Formatter("%(message)s"))
    logger.addHandler(logger_handler)

    # When worker number is set to -1 we max out the number of workers based
    # on Guinicorn assumptions: https://docs.gunicorn.org/en/stable/design.html#how-many-workers
    if workers == -1:
        workers = multiprocessing.cpu_count() * 2 + 1

    # Start mainloop.
    bjoern.listen(wsgi_application(), host, port)
    logger.info("Started server on %s:%d with %d workers.", host, port, workers)

    # Reconfigures logger so process ID is shown.
    logger_handler.setFormatter(logging.Formatter("[%(process)s] %(message)s"))

    # Start multiple processes with their own loggers.
    workers_pid = []
    for _ in range(workers):
        pid = os.fork()
        if pid > 0:
            workers_pid.append(pid)
        elif pid == 0:
            try:
                logger.info("Starting worker.")
                bjoern.run()
            except KeyboardInterrupt:
                exit()

    # Waits for the workers to finish.
    try:
        for _ in range(workers):
            os.wait()
    except KeyboardInterrupt:
        for pid in workers_pid:
            os.kill(pid, signal.SIGINT)


if __name__ == "__main__":
    start(host="127.0.0.1", port=8000, workers=1)