ZeroMQ

Handling Interrupt Signals

Realistic applications need to shut down cleanly when interrupted with Ctrl-C or another signal, such as SIGTERM. By default, these simply kill the process, meaning messages won’t be flushed, files won’t be closed cleanly, and so on.

Example 2-10 shows how we handle signals in various languages.

Example 2-10. Handling Ctrl-C cleanly (interrupt.c)

//
//  Shows how to handle Ctrl-C
//
#include <zmq.h>
#include <stdio.h>
#include <signal.h>

//  ---------------------------------------------------------------------
//  Signal handling
//
//  Call s_catch_signals() in your application at startup, and then exit
//  your main loop if s_interrupted is ever 1. Works especially well with 
//  zmq_poll.

static int s_interrupted = 0;
static void s_signal_handler (int signal_value)
{
    s_interrupted = 1;
}

static void s_catch_signals (void)
{
    struct sigaction action;
    action.sa_handler = s_signal_handler;
    action.sa_flags = 0;
    sigemptyset (&action.sa_mask);
    sigaction (SIGINT, &action, NULL);
    sigaction (SIGTERM, &action, NULL);
}

int main (void)
{
    void *context = zmq_ctx_new ();
    void *socket = zmq_socket (context, ZMQ_REP);
    zmq_bind (socket, "tcp://*:5555");

    s_catch_signals ();
    while (1) {
        //  Blocking read will exit on a signal
        zmq_msg_t message;
        zmq_msg_init (&message);
        zmq_msg_recv (&message, socket, 0);

        if (s_interrupted) {
            printf ("W: interrupt received, killing server...\n");
            break;
        }
    }
    zmq_close (socket);
    zmq_ctx_destroy (context);
    return 0;
}

The program provides s_catch_signals() ...