example poll program

urandompoll.c

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/poll.h>

#define TIMEOUT 5

int main (void)
{
        struct pollfd fds[1];
        int ret;

        int fd = open("/dev/urandom", O_RDWR);

        if (fd == -1) {
                perror ("open");
                return 1;
        }

        fds[0].fd = fd;
        fds[0].events = POLLIN|POLLOUT;

        ret = poll(fds, 1, TIMEOUT * 1000);

        if (ret == -1) {
                perror ("poll");
                return 1;
        }

        if (!ret) {
                printf ("%d seconds elapsed.\n", TIMEOUT);
                return 0;
        }

        if (fds[0].revents & POLLIN)
                printf ("urandom is readable\n");

        if (fds[0].revents & POLLOUT)
                printf ("urandom is writable\n");

        return 0;

}