example for synchronous signal processing with czmq/zloop using signalfd(2)

zsigfd.c

// example for synchronous signal processing with czmq/zloop using signalfd(2)
// Michael Haberler 1/2014

#include <czmq.h>
#include <sys/signalfd.h>

int signo;

static int s_handle_signal(zloop_t *loop, zmq_pollitem_t *poller, void *arg)
{
    struct signalfd_siginfo fdsi;
    ssize_t s = read(poller->fd, &fdsi, sizeof(struct signalfd_siginfo));
    if (s != sizeof(struct signalfd_siginfo)) {
	perror("read");
    }
    fprintf(stderr, "got ignal %d '%s'\n",fdsi.ssi_signo,strsignal(fdsi.ssi_signo) );
    signo = fdsi.ssi_signo;
    return -1; // exit reactor 
}

int main(int argc, char **argv)
{
    int sfd, retval;
    
    // suppress default handling of signals in zctx_new()
    // since we're using signalfd() - must happen before zctx_new()
    zsys_handler_set(NULL);
    
    void *ctx  = zctx_new();
    assert(ctx);

    zloop_t *loop = zloop_new();
    assert (loop);

    sigset_t sigmask;
    sigemptyset(&sigmask);

    // block all signal delivery through default signal handlers
    // since we're using signalfd()
    sigfillset(&sigmask);
    sigprocmask(SIG_SETMASK, &sigmask, NULL);

    // explicitly enable signals we want delivered via signalfd()
    sigemptyset(&sigmask);
    sigaddset(&sigmask, SIGINT);
    sigaddset(&sigmask, SIGQUIT);
    sigaddset(&sigmask, SIGTERM);
    sigaddset(&sigmask, SIGSEGV);
    sigaddset(&sigmask, SIGFPE);

    // only here it is safe to create threads with zthread() since
    // the sigmask is inherited from the main thread
    sfd = signalfd(-1, &sigmask, 0);
    
    assert(sfd != -1);

    zmq_pollitem_t signal_poller =  { 0, sfd,   ZMQ_POLLIN };
    zloop_poller (loop, &signal_poller, s_handle_signal, NULL);
   
    do {
	retval = zloop_start(loop);
    } while (!retval);

    if (signo) 
	fprintf(stderr, "exiting by signal %d\n", signo);

    exit(0);
}

changes:
Resetting the default signal handling with zsys_set_handler(NULL) must happen before a context is created.

Dont use side effects in assert() statements - in case this is compiled with -DNDEBUG .