Cycle a tornado server passing server fd (buggy)

tornado_passfd_demo.py

import os, sys, socket, passfd
import tornado.httpserver
import tornado.ioloop
import tornado.web
import time

class HelloHandler(tornado.web.RequestHandler):
    def get(self):
        self.write('hello from pid: %s' % os.getpid())

class SpawnHandler(tornado.web.RequestHandler):
    def get(self):
        from subprocess import Popen
        addr = '/tmp/tornado_fd'
        if os.path.exists(addr):
            os.remove(addr)
        p = Popen(['python', __file__, addr])
        while not os.path.exists(addr):
            time.sleep(0.01)
        time.sleep(0.1)
        ipc = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        ipc.connect(addr)
        passfd.sendfd(ipc, http_server._socket)
        assert ipc.recv(2) == 'OK'
        ipc.close()
        self.write('spawned')
        

app = tornado.web.Application([
    (r"/", HelloHandler),
    (r"/spawn", SpawnHandler),
])

if __name__ == '__main__':
    try:
        fd_pass_sock = sys.argv[1]
    except IndexError:
        fd = None
    else:
        ipc = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        ipc.bind(fd_pass_sock)
        ipc.listen(4)
        conn, addr = ipc.accept()
        fd = int(passfd.recvfd(conn)[0])
        conn.send('OK')
        conn.close()
        ipc.close()
    
    http_server = tornado.httpserver.HTTPServer(app)
    if fd:
        http_server._socket = socket.fromfd(fd, socket.AF_INET, socket.SOCK_STREAM)
    else:
        http_server.bind(8891)
    
    is_main = http_server.start(4)
    ioloop = tornado.ioloop.IOLoop.instance()
    ioloop.start()