Book Image

ZeroMQ

By : Faruk Akgul
Book Image

ZeroMQ

By: Faruk Akgul

Overview of this book

<p>ØMQ (also spelled ZeroMQ, 0MQ, or ZMQ) is 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 ØMQ system can run without a dedicated message broker. The library is designed to have a familiar socket-style API.<br /><br />"ZeroMQ" teaches you to use ZeroMQ through examples in C programming language. You will learn how to use fundamental patterns of message/queuing with a step-by-step tutorial approach and how to apply them. Then, you’ll learn how to use high level APIs and to work with multiple sockets and multithreaded programs through many examples.<br /><br />This book looks at how message/queue works in general and what kinds of problems it solves. Then, it explains how ZeroMQ works and how it differs from other message/queue libraries and how it can be used in different scenarios.<br /><br />You will also learn how to apply essential message/queue design patterns in different scenarios, and how they differ from each other. It shows you practical examples you can apply. You will also learn how to work with multiple sockets.<br /><br />You will learn the basics of ZeroMQ as well as how to use different patterns.</p>
Table of Contents (12 chapters)

Working with multi-part messages


We always define messages using zmq_msg. When we want to send multi-part messages, again, we need to use zmq_msg. For example, if the data package is divided into 10 parts, you need to create 10 zmq_msg sockets. The client either receives all the message parts or nothing at all. In order to send multi-part messages, the ZMQ_SNDMORE flag must be set during the zmq_send call.

int zmq_send(void* socket, void* buf, size_t len, int flags);

The following is the request-reply example that we used in Chapter 1, Getting Started, but this time we will send the message in multiple parts. First, let's have a look at the server code:

/*

  Request - Reply
  
  Send "world" in multiple-parts.

  server.c

*/

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

int main (int argc, char const *argv[]) {
  
  void* context = zmq_ctx_new();
  void* respond = zmq_socket(context, ZMQ_REP);
  zmq_bind(respond, "tcp://*:4040");

  printf...