zmq.error.ZMQError: Address already in use

1、如下代码，启动的时候python app.py会报如题的错误

app.py

#!/user/bin python
# -*- coding:utf-8 -*- 


import os
from datetime import timedelta
from flask import Flask, session, url_for, render_template, make_response, request, redirect
import zerorpcimport multiprocessing


APP = Flask(__name__)
APP.secret_key = os.urandom(24)
APP.permanent_session_lifetime = timedelta(seconds=30 * 24 * 60 * 60)

class RPCServer(object):
    def hello(self, filename):
　　　　　　return filename





@APP.route('/')
@APP.route('/index')
def index():
    return render_template('index.html')


@APP.route('/ok.htm',methods=['GET', 'POST','HEAD'])
def ok():
    return render_template('ok.htm')


@APP.route('/test')
def test():
    session.permanent = True
    _str = ''
    if 'name' in session:
        _str = session['name']
    if 'nick' in session:
        _str += '---' + session['nick']
    #print session
    return _str


def runWeb():
    print ("start webapp")
    APP.run(host='0.0.0.0', port= 5000, debug=True, threaded=True)



def runRPC():
    #print "start rpc"
    s = zerorpc.Server(RPCServer())
    s.bind("tcp://0.0.0.0:4242")
    s.run()


if __name__ == "__main__":
    p1 = multiprocessing.Process(target = runWeb)
    p2 = multiprocessing.Process(target = runRPC)

    p1.start()
    p2.start()
    p1.join()
    p2.join()

    # p1.run()
    # p2.run()

    # p1.join()
    # p2.join()