zeroMQ初体验-2.发布订阅模式(pub/sub)

pub/sub模式：

[img]http://github.com/imatix/zguide/raw/master/images/fig4.png[/img]

发布端(pub)

import itertools
import sys  
import time 

import zmq  

def main(): 
    if len (sys.argv) != 2:
        print 'usage: publisher '
        sys.exit (1)

    bind_to = sys.argv[1]

    all_topics = ['sports.general','sports.football','sports.basketball',
                  'stocks.general','stocks.GOOG','stocks.AAPL',
                  'weather']

    ctx = zmq.Context()
    s = ctx.socket(zmq.PUB)
    s.bind(bind_to)

    print "Starting broadcast on topics:"
    print "   %s" % all_topics
    print "Hit Ctrl-C to stop broadcasting."
    print "Waiting so subscriber sockets can connect..."
    print
    time.sleep(1.0)

    msg_counter = itertools.count()
    try:
        for topic in itertools.cycle(all_topics):
            msg_body = str(msg_counter.next())
            print '   Topic: %s, msg:%s' % (topic, msg_body)
            #s.send_multipart([topic, msg_body])
            s.send_pyobj([topic, msg_body])
            # short wait so we don't hog the cpu
            time.sleep(0.1)
    except KeyboardInterrupt:
        pass

    print "Waiting for message queues to flush..."
    time.sleep(0.5)
    s.close()
    print "Done."

if __name__ == "__main__":
    main()

订阅端(sub):

import sys
import time
import zmq

def main():
    if len (sys.argv) < 2:
        print 'usage: subscriber  [topic topic ...]'
        sys.exit (1)

    connect_to = sys.argv[1]
    topics = sys.argv[2:]

    ctx = zmq.Context()
    s = ctx.socket(zmq.SUB)
    s.connect(connect_to)

    # manage subscriptions
    if not topics:
        print "Receiving messages on ALL topics..."
        s.setsockopt(zmq.SUBSCRIBE,'')
    else:
        print "Receiving messages on topics: %s ..." % topics
        for t in topics:
            s.setsockopt(zmq.SUBSCRIBE,t)
    print
    try:
        while True:
            #topic, msg = s.recv_multipart()
            topic, msg = s.recv_pyobj()
            print '   Topic: %s, msg:%s' % (topic, msg)
    except KeyboardInterrupt:
        pass
    print "Done."

if __name__ == "__main__":
    main()

注意：
这里的发布与订阅角色是绝对的，即发布者无法使用recv,订阅者不能使用send,并且订阅者需要设置订阅条件"setsockopt"。
按照官网的说法，在这种模式下很可能发布者刚启动时发布的数据出现丢失，原因是用zmq发送速度太快，在订阅者尚未与发布者建立联系时，已经开始了数据发布(内部局域网没这么夸张的)。官网给了两个解决方案;1,发布者sleep一会再发送数据(这个被标注成愚蠢的);2,(还没有看到那，在后续中发现的话会更新这里)。
官网还提供了一种可能出现的问题：当订阅者消费慢于发布，此时就会出现数据的堆积，而且还是在发布端的堆积(有朋友指出是堆积在消费端，或许是新版本改进，需要读者的尝试和反馈，thx!)，显然，这是不可以被接受的。至于解决方案，或许后面的"分而治之"就是吧。

(未完待续)