selectorbug.py

import asyncio
import socket
from contextlib import suppress
from pprint import pprint


async def main():
    async def send_loop():
        payload = b'\x00' * 1024_000
        while True:
            await loop.sock_sendall(client_sock, payload)

    print('selector keys in the beginning:')
    pprint(loop._selector._fd_to_key)
    print()

    serv_sock = socket.socket()
    serv_sock.setblocking(False)
    serv_sock.bind(('127.0.0.1', 0))
    serv_sock.listen()

    for _ in range(2):
        client_sock = socket.socket()
        client_sock.setblocking(False)
        print(f'connecting fd {client_sock.fileno()} to', serv_sock.getsockname())
        connect_task = loop.create_task(loop.sock_connect(client_sock, serv_sock.getsockname()))
        conn, addr = await loop.sock_accept(serv_sock)
        print(f'connection accepted in fd {conn.fileno()}')
        await connect_task
        print('connected')

        # Wait for send_loop() to be blocked
        send_task = loop.create_task(send_loop())
        while send_task._coro.cr_await is None:
            await asyncio.sleep(0)

        send_task.cancel()
        print('closing fd', client_sock.fileno())
        client_sock.close()
        conn.close()
        with suppress(asyncio.CancelledError):
            await send_task

        print('selector keys after the client has been closed:')
        pprint(loop._selector._fd_to_key)
        print()


loop = asyncio.get_event_loop()
loop.run_until_complete(main())