vic-txZMQ 0.5.2

Twisted bindings for ZeroMQ

Contents

• Introduction

• Improvement

• Requirements

• Details

• Example

• Hacking

Introduction

Note

This is not the original version of txZMQ, this is a refactoried version of txZMQ by Victor Lin.

txZMQ allows to integrate easily 0MQ sockets into Twisted event loop (reactor).

txZMQ supports both CPython and PyPy.

Improvement

Original API design of txZMQ was wrongly designed, and they are not reusable or hard to use, for example, to set HWM of a ZeroMQ socket, you need to change the class level variable.:

from txzmq import ZmqConnection
ZmqConnection.highWaterMark = 100
conn = ZmqConnection(factory)

As you can see the highWaterMark variable affects all connection made afterward. This is obviously not a good design.

Also, the encapsulation of endpoints is not necessary. Sometimes you may need to connect or bind a address after a ZmqConnection was created, original design has no obvious way to do it. You need to pass endpoints when create a new ZmqConnection.

PUSH/PULL and PAIR connections are not present in original version. I add those connection types in this library.

There is also a serious bug in original version. When read signal of FD is triggered before reactor perform another select, then txZMQ stop reading from that socket anymore. This version fixes the bug.

Requirements

Non-Python library required:

• 0MQ library >= 2.1 (heavily tested with 2.1.4)

Python packages required:

• pyzmq (for CPython)

• pyzmq-ctypes (for PyPy)

• Twisted

Details

txZMQ introduces support for general 0MQ sockets by class ZmqConnection that can do basic event loop integration, sending-receiving messages in non-blocking manner, scatter-gather for multipart messages.

txZMQ uses ØMQ APIs to get file descriptor that is used to signal pending actions from ØMQ library IO thread running in separate thread. This is used in a custom file descriptor reader, which is then added to the Twisted reactor.

From this class, one may implement the various patterns defined by 0MQ. For example, special descendants of the ZmqConnection class, ZmqPubConnection and ZmqSubConnection, add special nice features for PUB/SUB sockets.

Request/reply pattern is achieved via XREQ/XREP sockets and classes ZmqXREQConnection, ZmqXREPConection.

Push/pull pattern is achieved via classes ZmqPushConnection, ZmqPullConection.

Finally, Pair pattern is achieved via classes ZmqPairConnection.

Example

Here is an example of using txZMQ:

import os
import sys
import time
from optparse import OptionParser

from twisted.internet import reactor

import zmq
from txzmq import ZmqFactory, ZmqPubConnection, ZmqSubConnection

parser = OptionParser("")
parser.add_option("-m", "--method", dest="method", help="0MQ socket connection: bind|connect")
parser.add_option("-e", "--endpoint", dest="endpoint", help="0MQ Endpoint")
parser.add_option("-M", "--mode", dest="mode", help="Mode: publisher|subscriber")
parser.set_defaults(method="connect", endpoint="epgm://eth1;239.0.5.3:10011")

(options, args) = parser.parse_args()

zf = ZmqFactory()

def bind_or_connect(s):
    if options.method == 'bind':
        s.bind(options.endpoint)
    elif options.method == 'connect':
        s.connect(options.endpoint)

if options.mode == "publisher":
    pub = ZmqPubConnection(zf)
    bind_or_connect(pub)

    def publish():
        data = str(time.time())
        print "publishing %r" % data
        pub.send(data)

        reactor.callLater(1, publish)

    publish()
else:
    def doPrint(msgs):
        print "message received: %r" % (msgs, )
    sub = ZmqSubConnection(zf, callback=doPrint)
    sub.setsockopt(zmq.SUBSCRIBE, '')
    bind_or_connect(sub)

reactor.run()

The same example is available in the source code. You can run it from the checkout directory with the following commands (in two different terminals):

examples/pub_sub.py --method=bind --endpoint=ipc:///tmp/sock --mode=publisher

examples/pub_sub.py --method=connect --endpoint=ipc:///tmp/sock --mode=subscriber

Hacking

Source code for txZMQ is available at github; forks and pull requests are welcome.

To start hacking, fork at github and clone to your working directory. To use the Makefile (for running unit tests, checking for PEP8 compliance and running pyflakes), you will want to have virtualenv installed (it includes a pip installation).

Create a branch, add some unit tests, write your code, check it and test it! Some useful make targets are:

• make env

• make check

• make test

If you don’t have an environment set up, a new one will be created for you in ./env. Additionally, txZMQ will be installed as well as required development libs.