0MQ – Introduction

0MQ (also spelled ZeroMQ, 0MQ or ZMQ) was originally a high-performance asynchronous messaging library aimed at use in scalable distributed or concurrent applications. It provides a message queue, but unlike message-oriented middleware, a 0MQ system can run without a dedicated message broker. The library is designed to have a familiar socket-style API, and was developed by iMatix Corporation.

How to install

ZeroMQ comes as source code licensed under LGPLv3+, which can be got from ZeroMQ. For the papers, ZeroMQ 3.2.3 is used to show the feature and source code.

Here are quick steps to install the ZMQ:

Get the source code tar from the offical web site:

wget http://download.zeromq.org/zeromq-3.2.3.tar.gz

Decompress the tar to get the source code:

tar zxvf zeromq-3.2.3.tar.gz

Generate the Makefiles by autotools:

./configure --enable-debug --prefix=/opt/zmq

–enable-debug is not necessary; it will enable debug information, so gdb works.

Build and install the software:

make && make install

Check the directory:

/opt/zmq
    |-include
        |-lib
            |-share
                    |-man

Samples

Here is a sample to show ZMQ’s basic APIs and how it works; and based on this sample, let show

  • how data exchanged between server and client
  • how many threads are started
  • how server/client works
  • what’s technology used
  • ….

Server code:

#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>

int main (void)
{
    // Socket to talk to clients
    void *context = zmq_ctx_new ();
    void *responder = zmq_socket (context, ZMQ_REP);
    int rc = zmq_bind (responder, "tcp://*:5555");
    assert (rc == 0);
    while (1) {
        char buffer [10];
        zmq_recv (responder, buffer, 10, 0);
        printf ("Received Hello\n");
        zmq_send (responder, "World", 5, 0);
        sleep (1);
        // Do some 'work'
    }
    return 0;
}

Client code:

#include <zmq.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>

int main (void)
{
    printf ("Connecting to hello world server...\n");
    void *context = zmq_ctx_new ();
    void *requester = zmq_socket (context, ZMQ_REQ);
    zmq_connect (requester, "tcp://localhost:5555");

    int request_nbr;
    for (request_nbr = 0; request_nbr != 2; request_nbr++) {
        char buffer [10];
        printf ("Sending Hello %d...\n", request_nbr);
        zmq_send (requester, "Hello", 5, 0);
        zmq_recv (requester, buffer, 10, 0);
        printf ("Received World %d\n", request_nbr);
    }
    zmq_close (requester);
    zmq_ctx_destroy (context);
    return 0;
}

Makefile:

all:
    g++ -g server.cpp -o serv -I/opt/zmq/include/ -L/opt/zmq/lib -lzmq
    g++ -g client.cpp -o client -I/opt/zmq/include/ -L/opt/zmq/lib -lzmq

Output:

Connecting to hello world server...
Sending Hello 0...
Received Hello
Received World 0
Sending Hello 1...
Received Hello
Received World 1
Written on June 5, 2013