#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

int received;

void
handler(int sig, siginfo_t *si, void *ctx)
{
        if (si->si_code != SI_QUEUE)
                errx(1, "si_code != SI_QUEUE");
        if (si->si_value.sival_int != received)
                errx(1, "signal is out of order");
        received++;
}

int
main()
{
        struct sigaction sa;
        union sigval val;
        int ret;
        int i;
        sigset_t set;

        sa.sa_flags = SA_SIGINFO;
        sigemptyset(&sa.sa_mask);
        sa.sa_sigaction = handler;
        sigaction(SIGRTMIN, &sa, NULL);
        sigemptyset(&set);
        sigaddset(&set, SIGRTMIN);
        sigprocmask(SIG_BLOCK, &set, NULL);
        i = 0;
        for (;;) {
                val.sival_int = i;
                ret = sigqueue(getpid(), SIGRTMIN, val);
                if (ret == -1) {
                        if (errno != EAGAIN) {
                                errx(1, "errno != EAGAIN");
                        }
                        break;
                }
                i++;
        }
        sigprocmask(SIG_UNBLOCK, &set, NULL);
        if (received != i)
                errx(1, "error, signal lost");
        printf("OK\n");
}