Twisted error in server with mqtt client - twisted

Question

I'm running a Twisted TCP server. Each protocol instance has an mqtt pub/sub client. I've reduced the actual production code to the simplest possible form below. I've stripped out a lot of irrelevant complexity to simplify the bug-finding process. The server works for multiple client connections and produces the data received from the mqtt client, but after any client connects/disconnects/reconnects a few times I get an exception that I haven't been able to understand or trap. I'm hoping that Jean-Paul or someone can point me at the error of my ways.
Once the exception occurs, no new clients can connect to the server. Each new connect attempt produces the exception.
Clients that are already connected continue to receive data ok.
The exception is
Unhandled Error
Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/twisted/python/log.py", line 73, in callWithContext
return context.call({ILogContext: newCtx}, func, *args, **kw)
File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext
return self.currentContext().callWithContext(ctx, func, *args, **kw)
File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext
return func(*args,**kw)
File "/usr/lib/python2.7/dist-packages/twisted/internet/posixbase.py", line 614, in _doReadOrWrite
why = selectable.doRead()
--- <exception caught here> ---
File "/usr/lib/python2.7/dist-packages/twisted/internet/tcp.py", line 1069, in doRead
transport = self.transport(skt, protocol, addr, self, s, self.reactor)
File "/usr/lib/python2.7/dist-packages/twisted/internet/tcp.py", line 786, in __init__
self.startReading()
File "/usr/lib/python2.7/dist-packages/twisted/internet/abstract.py", line 429, in startReading
self.reactor.addReader(self)
File "/usr/lib/python2.7/dist-packages/twisted/internet/epollreactor.py", line 256, in addReader
_epoll.EPOLLIN, _epoll.EPOLLOUT)
File "/usr/lib/python2.7/dist-packages/twisted/internet/epollreactor.py", line 240, in _add
self._poller.modify(fd, flags)
exceptions.IOError: [Errno 2] No such file or directory
The basic server code is:
(this example will run and does generate the exception)
from twisted.internet import reactor
from twisted.internet.protocol import Factory
from twisted.protocols import basic
from paho.mqtt import client # The most recent version of the legacy Mosquitto client
from random import randint
class MsgReceiver(basic.LineReceiver):
def __init__(self, factory): # new (factory)
self.factory = factory # new (factory)
def connectionMade(self):
self.mqClient = self.startMQ()
if self.mqClient:
self.factory.clients.append(self)
else:
self.transport.loseConnection()
def connectionLost(self, reason):
pass
def lineReceived(self, line):
pass
def on_message(self, mosq, obj, msg):
try:
self.sendLine(msg.payload)
except Exception, err:
print(err.message)
def startMQ(self):
mqName = "-".join(["myAppName", str(randint(0, 99999))])
mqClient = client.Client(mqName)
if mqClient.connect("localhost", 1883, 60) != 0:
print('Could not connect to mq server')
return False
mqClient.on_message = self.on_message
(success, mid) = mqClient.subscribe("myTopic", 0)
if success != 0:
return False
mqClient.loop_start()
return mqClient
class MsgReceiverFactory(Factory):
allow_reuse_address = True
def __init__(self, clients):
self.clients = clients
def buildProtocol(self, addr):
return MsgReceiver(self)
if __name__ == "__main__":
try:
clients = []
reactor.listenTCP(43217, MsgReceiverFactory(clients))
reactor.run()
except Exception, err:
print(err.message)
if reactor.running:
reactor.stop()
A simple client that will induce the error when run twice (the first time it runs fine):
Interesting that if I enable the time.sleep(3) it runs fine and doesn't seem to induce the error
#!/usr/bin/python
from __future__ import print_function
import socket
import time
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("localhost", 43217))
data = s.recv(1024)
print(data)
#time.sleep(3)
s.close()