#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <stdio.h>

extern "C" {

typedef void (*sig_handler_t)(int);

void sig_handler (int s)
{
    // re-register
    signal (s, sig_handler);
}

} // extern "C"

int main ()
{
    const pid_t pid = fork ();
    if (0 == pid) {
        sleep (3);
    }
    else {

        sig_handler_t old_handler = signal (SIGCHLD, sig_handler);

        // wait 5 seconds for child to exit
        unsigned wait = 5;

        do {
            int status = 0;

            const pid_t ret = waitpid (pid, &status, WNOHANG);
            if (ret < 0) {
                fprintf (stderr, "failed waiting for child!\n");
                return 1;
            }
            else if (0 == ret) {
                // child still alive, wait a little while
                fprintf (stdout, "waiting...\n");
                wait = sleep (wait);

                // try again
                continue;
            }
            else {
                // child exited
            }

        } while (0);

        signal (SIGCLD, old_handler);
    }

    return 0;
}