如何阻止ZeroMQ服务器接受多个连接？

Question

我有一台ZeroMQ（PAIR）服务器，但如果有多个客户端连接到服务器，则服务器会崩溃并显示以下消息：

Assertion failed: !inpipe && !outpipe (pair.cpp:49)

如何防止这种情况？我的服务器代码使用txzmq：

from txzmq import ZmqEndpoint, ZmqFactory
from twisted.internet import reactor, protocol, task
from txzmq.connection import ZmqConnection
from zmq import constants

class PairConnection(ZmqConnection):

    socketType = constants.PAIR

    # Send a message to the drone
    def messageSend(self, message):
        print "Sending:", message
        self.send(message)

    # Receive a message from the drone.
    def messageReceived(self, message):      
        print message

factory_zmq = ZmqFactory()
factory_zmq.protocol = PairConnection(factory_zmq, ZmqEndpoint("bind", "tcp://*:5500")) 
reactor.run()