foo.py

import asyncio
import functools
import os
import signal
import socket
import websockets
from multiprocessing import Process
from pathlib import Path

# this is set by the parent, and inherited by the children
sock = None


async def handler(*args, **kwargs):
    while True:
        print("being handled")
        await asyncio.sleep(1)


async def setup():
    event = asyncio.Event()

    server = websockets.unix_serve(
        handler,
        # this path argument is REQUIRED by websockets to branch to create_unix_server
        # but we don't actually want to specify a path, because we're passing in the `sock` instead.
        # Python blocks us from specifying both:
        # https://github.com/python/cpython/blob/66d3b589c44fcbcf9afe1e442d9beac3bd8bcd34/Lib/asyncio/unix_events.py#L245
        path="thisisnotused",
        sock=sock,
        close_timeout=.2,
        max_size=2**16,
        compression=None,
        backlog=65535)

    # hack to strip the `path` argument (uncomment to make it work)
    # partial = server._create_server
    # server._create_server = functools.partial(partial.func, *partial.args[:-1], **partial.keywords)

    async with server:
        print("Started server")
        await event.wait()
    print("Exiting")


def child():
    asyncio.get_event_loop().run_until_complete(setup())


if __name__ == "__main__":
    # create the socket in the parent
    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
    socket_path = Path(__file__).parent / "ws_server.sock"
    try:
        os.unlink(socket_path)
    except FileNotFoundError:
        pass

    sock.bind(str(socket_path))
    sock.listen(65535)
    sock.setblocking(False)
    # just so we don't have any errors during debugging
    os.chmod(str(socket_path), 0o777)

    workers = []
    # these child processes will inherit the listening socket
    # on unix because of the fork() system call
    for i in range(2):
        p = Process(target=child)
        p.start()
        workers.append(p)

    for p in workers:
        p.join()

    print("Parent exiting")