ZeroMQ

ROUTER Broker and REQ Workers

Example 3-2 is an example of the load-balancing pattern using a ROUTER broker talking to a set of REQ workers.

Example 3-2. ROUTER-to-REQ (rtreq.c)

//
//  ROUTER-to-REQ example
//
#include "zhelpers.h"
#include <pthread.h>

#define NBR_WORKERS 10

static void *
worker_task (void *args)
{
    void *context = zmq_ctx_new ();
    void *worker = zmq_socket (context, ZMQ_REQ);
    s_set_id (worker);          //  Set a printable identity
    zmq_connect (worker, "tcp://localhost:5671");

    int total = 0;
    while (1) {
        //  Tell the broker we're ready for work
        s_send (worker, "Hi Boss");

        //  Get workload from broker, until finished
        char *workload = s_recv (worker);
        int finished = (strcmp (workload, "Fired!") == 0);
        free (workload);
        if (finished) {
            printf ("Completed: %d tasks\n", total);
            break;
        }
        total++;

        //  Do some random work
        s_sleep (randof (500) + 1);
    }
    zmq_close (worker);
    zmq_ctx_destroy (context);
    return NULL;
}

While this example runs in a single process, that is only to make it easier to start and stop. Each thread has its own context and conceptually acts as a separate process. Example 3-3 shows the main task.

Example 3-3. ROUTER-to-REQ (rtreq.c): main task

int main (void)
{
    void *context = zmq_ctx_new ();
    void *broker = zmq_socket (context, ZMQ_ROUTER);

    zmq_bind (broker, "tcp://*:5671");
    srandom ((unsigned) time (NULL));

    int worker_nbr;
    for (worker_nbr = 0; worker_nbr < NBR_WORKERS; worker_nbr++) {
        pthread_t worker;
        pthread_create (&worker, NULL, worker_task, NULL);
    }
    // Run for five seconds ...