Creating a AsyncHTTPClient object in a class causes FileNotFound Error - python-3.x

Question

When I try to make the HTTP client a class variable of my tcp server class I see the following error:
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "cisco-dial-out-mdt-async-client.py", line 208, in <module>
tcp_server.start(0)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/tcpserver.py", line 244, in start
self.add_sockets(sockets)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/tcpserver.py", line 166, in add_sockets
sock, self._handle_connection
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/netutil.py", line 279, in add_accept_handler
io_loop.add_handler(sock, accept_handler, IOLoop.READ)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/platform/asyncio.py", line 99, in add_handler
self.asyncio_loop.add_reader(fd, self._handle_events, fd, IOLoop.READ)
File "/usr/lib/python3.7/asyncio/selector_events.py", line 324, in add_reader
return self._add_reader(fd, callback, *args)
File "/usr/lib/python3.7/asyncio/selector_events.py", line 254, in _add_reader
child 13 (pid 3260) killed by signal 2, restarting
(handle, None))
File "/usr/lib/python3.7/selectors.py", line 359, in register
Traceback (most recent call last):
File "cisco-dial-out-mdt-async-client.py", line 208, in <module>
self._selector.register(key.fd, poller_events)
Traceback (most recent call last):
FileExistsError: [Errno 17] File exists
File "/usr/lib/python3.7/asyncio/selector_events.py", line 251, in _add_reader
tcp_server.start(0)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/tcpserver.py", line 241, in start
process.fork_processes(num_processes, max_restarts)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/process.py", line 175, in fork_processes
key = self._selector.get_key(fd)
raise RuntimeError("Too many child restarts, giving up")
File "/usr/lib/python3.7/selectors.py", line 192, in get_key
RuntimeError: Too many child restarts, giving up
raise KeyError("{!r} is not registered".format(fileobj)) from None
KeyError: '9 is not registered'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "cisco-dial-out-mdt-async-client.py", line 208, in <module>
tcp_server.start(0)
Traceback (most recent call last):
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/tcpserver.py", line 244, in start
File "/usr/lib/python3.7/asyncio/selector_events.py", line 251, in _add_reader
self.add_sockets(sockets)
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/tcpserver.py", line 166, in add_sockets
key = self._selector.get_key(fd)
File "/usr/lib/python3.7/selectors.py", line 192, in get_key
sock, self._handle_connection
File "/home/lab/venv3.7/lib/python3.7/site-packages/tornado/netutil.py", line 279, in add_accept_handler
raise KeyError("{!r} is not registered".format(fileobj)) from None
KeyError: '9 is not registered'
When I remove the line that creates the object it works fine
class TelemetryTCPDialOutServer(TCPServer):
def __init__(self, elasticsearch_server):
super().__init__()
self.elastic_server = elasticsearch_server
self.lock = Lock()
log_name = __file__.strip('.py')
self.log = self.init_log(f"{log_name}.log")
self.lock = Lock()
self.http_client = AsyncHTTPClient() <== This line
Is it possible to put the http client in the class or make it a local object to some of the class functions. (This way works too).
Thansk

Answer 1

It looks like something has really messed up your stack trace, but I think the problem is that you're calling tcp_server.start(0) too late. start(0) forks multiple child processes, and it's invalid to fork multiple processes once the event loop has been created.
If you can, move this start(0) call earlier (typically it's the first thing you do after processing your command line or config file). If you can't move it earlier, you'll have to split up the process creation from starting the server. This is the "advanced multi-process" pattern from https://www.tornadoweb.org/en/stable/tcpserver.html:
# This part comes very early, just after processing configs
sockets = bind_sockets(8888)
tornado.process.fork_processes(0)
# This part can come later
server = TCPServer()
server.add_sockets(sockets)
IOLoop.current().start()