ZeroMQ快速入门

本文主要参考guotianqing的CSDN博客：ZeroMQ基础入门和官方文档

ZeroMQ是一个轻量级消息通信库，扩展传统的标准socket接口。提供了异步消息队列的抽象，能够实现消息过滤，能够无缝对接多种传输协议。其中MQ是消息队列（Message Queue）的缩写。其官方介绍如下：

ZeroMQ (also known as ØMQ, 0MQ, or zmq) looks like an embeddable networking library but acts like a concurrency framework. It gives you sockets that carry atomic messages across various transports like in-process, inter-process, TCP, and multicast. You can connect sockets N-to-N with patterns like fan-out, pub-sub, task distribution, and request-reply. It's fast enough to be the fabric for clustered products. Its asynchronous I/O model gives you scalable multicore applications, built as asynchronous message-processing tasks. It has a score of language APIs and runs on most operating systems.

ZMQ支持常见的三种基本通信模式，分别是Pub/Sub、Req/Rep、Push/Pull。比较重要的类型有：zmq::context_t，zmq::socket_t和zmq::message_t。比较重要的方法则包括：socket_t::send(message_t)，socket_t::recv(&message_t)和socket_t::setsockopt()等。

Req/Rep

Request-Reply

服务端（响应端ZMQ_REP）：

//
//  Hello World server in C++
//  Binds REP socket to tcp://*:5555
//  Expects "Hello" from client, replies with "World"
//
#include 
#include 
#include 
#ifndef _WIN32
#include 
#else
#include 

#define sleep(n)    Sleep(n)
#endif

int main () {
    //  Prepare our context and socket
    zmq::context_t context (1);
    zmq::socket_t socket (context, ZMQ_REP);
    socket.bind ("tcp://*:5555");

    while (true) {
        zmq::message_t request;

        //  Wait for next request from client
        socket.recv (&request);
        std::cout << "Received Hello" << std::endl;

        //  Do some 'work'
        sleep(1);

        //  Send reply back to client
        zmq::message_t reply (5);
        memcpy (reply.data (), "World", 5);
        socket.send (reply);
    }
    return 0;
}

客户端（请求端ZMQ_REQ）：

//
//  Hello World client in C++
//  Connects REQ socket to tcp://localhost:5555
//  Sends "Hello" to server, expects "World" back
//
#include 
#include 
#include 

int main ()
{
    //  Prepare our context and socket
    zmq::context_t context (1);
    zmq::socket_t socket (context, ZMQ_REQ);

    std::cout << "Connecting to hello world server…" << std::endl;
    socket.connect ("tcp://localhost:5555");

    //  Do 10 requests, waiting each time for a response
    for (int request_nbr = 0; request_nbr != 10; request_nbr++) {
        zmq::message_t request (5);
        memcpy (request.data (), "Hello", 5);
        std::cout << "Sending Hello " << request_nbr << "…" << std::endl;
        socket.send (request);

        //  Get the reply.
        zmq::message_t reply;
        socket.recv (&reply);
        std::cout << "Received World " << request_nbr << std::endl;
    }
    return 0;
}

对于字符串，需要注意的一点是，ZMQ不会关心发送消息的内容，只要知道它所包含的字节数。这意味着，ZMQ的字符串是有长度的，且传送时不加结束符。当使用c语言接收时，应注意申请比长度多一个字节的存储空间，并置位结束符’/0’，否则在打印字符串时可能得到奇怪的结果。

Pub/Sub

Publish-Subscribe

服务端（发布端ZMQ_PUB）：

//  Weather update server in C++
//  Binds PUB socket to tcp://*:5556
//  Publishes random weather updates
//
//  Olivier Chamoux 
//
#include 
#include 
#include 
#include 

#if (defined (WIN32))
#include 
#endif

#define within(num) (int) ((float) num * random () / (RAND_MAX + 1.0))

int main () {

    //  Prepare our context and publisher
    zmq::context_t context (1);
    zmq::socket_t publisher (context, ZMQ_PUB);
    publisher.bind("tcp://*:5556");
    publisher.bind("ipc://weather.ipc");                // Not usable on Windows.

    //  Initialize random number generator
    srandom ((unsigned) time (NULL));
    while (1) {

        int zipcode, temperature, relhumidity;

        //  Get values that will fool the boss
        zipcode     = within (100000);
        temperature = within (215) - 80;
        relhumidity = within (50) + 10;

        //  Send message to all subscribers
        zmq::message_t message(20);
        snprintf ((char *) message.data(), 20 ,
            "%05d %d %d", zipcode, temperature, relhumidity);
        publisher.send(message);

    }
    return 0;
}

客户端（订阅端ZMQ_SUB）：

//  Weather update client in C++
//  Connects SUB socket to tcp://localhost:5556
//  Collects weather updates and finds avg temp in zipcode
//
//  Olivier Chamoux 
//
#include 
#include 
#include 

int main (int argc, char *argv[])
{
    zmq::context_t context (1);

    //  Socket to talk to server
    std::cout << "Collecting updates from weather server…\n" << std::endl;
    zmq::socket_t subscriber (context, ZMQ_SUB);
    subscriber.connect("tcp://localhost:5556");

    //  Subscribe to zipcode, default is NYC, 10001
    const char *filter = (argc > 1)? argv [1]: "10001 ";
    subscriber.setsockopt(ZMQ_SUBSCRIBE, filter, strlen (filter));

    //  Process 100 updates
    int update_nbr;
    long total_temp = 0;
    for (update_nbr = 0; update_nbr < 100; update_nbr++) {

        zmq::message_t update;
        int zipcode, temperature, relhumidity;

        subscriber.recv(&update);

        std::istringstream iss(static_cast(update.data()));
        iss >> zipcode >> temperature >> relhumidity ;

        total_temp += temperature;
    }
    std::cout     << "Average temperature for zipcode '"<< filter
                <<"' was "<<(int) (total_temp / update_nbr) <<"F"
                << std::endl;
    return 0;
}

需要注意的是，在使用SUB套接字时，必须使用setsockopt()方法来设置订阅的内容。该方法可以用于设置消息过滤器，但如果你不设置订阅内容，那将什么消息都收不到。订阅信息可以是任何字符串，可以设置多次。只要消息满足其中一条订阅信息，SUB套接字就会收到。订阅者可以选择不接收某类消息，也是通过setsockopt()方法实现的。

Push/Pull

push/pull

其他参考

https://github.com/booksbyus/zguide/tree/master/examples/C%2B%2B