Testing, how signals are handled when not blocked for handler execution time

signal_handling.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>

void action_usr1 (int sig)
{
        sleep (3);
        puts ("usr1");
        fflush (stdout);
}

struct sigaction act = {
        .sa_handler = action_usr1,
        .sa_flags = SA_NODEFER
};

int main (int argc, char ** argv)
{
        sigaction (SIGUSR1, & act, NULL);

        puts ("oh, hello");
        while (1)
                sleep (1);
        return EXIT_SUCCESS;
}