source: azure_iot_hub/trunk/musl-1.1.18/src/mq/mq_notify.c@ 388

#include <mqueue.h>
#include <pthread.h>
#include <errno.h>
#include <sys/socket.h>
#include <signal.h>
#include <unistd.h>
#include "syscall.h"

struct args {
        pthread_barrier_t barrier;
        int sock;
        const struct sigevent *sev;
};

static void *start(void *p)
{
        struct args *args = p;
        char buf[32];
        ssize_t n;
        int s = args->sock;
        void (*func)(union sigval) = args->sev->sigev_notify_function;
        union sigval val = args->sev->sigev_value;

        pthread_barrier_wait(&args->barrier);
        n = recv(s, buf, sizeof(buf), MSG_NOSIGNAL|MSG_WAITALL);
        close(s);
        if (n==sizeof buf && buf[sizeof buf - 1] == 1)
                func(val);
        return 0;
}

int mq_notify(mqd_t mqd, const struct sigevent *sev)
{
        struct args args = { .sev = sev };
        pthread_attr_t attr;
        pthread_t td;
        int s;
        struct sigevent sev2;
        static const char zeros[32];

        if (!sev || sev->sigev_notify != SIGEV_THREAD)
                return syscall(SYS_mq_notify, mqd, sev);

        s = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, 0);
        if (s < 0) return -1;
        args.sock = s;

        if (sev->sigev_notify_attributes) attr = *sev->sigev_notify_attributes;
        else pthread_attr_init(&attr);
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
        pthread_barrier_init(&args.barrier, 0, 2);

        if (pthread_create(&td, &attr, start, &args)) {
                __syscall(SYS_close, s);
                errno = EAGAIN;
                return -1;
        }

        pthread_barrier_wait(&args.barrier);
        pthread_barrier_destroy(&args.barrier);

        sev2.sigev_notify = SIGEV_THREAD;
        sev2.sigev_signo = s;
        sev2.sigev_value.sival_ptr = (void *)&zeros;

        if (syscall(SYS_mq_notify, mqd, &sev2) < 0) {
                pthread_cancel(td);
                __syscall(SYS_close, s);
                return -1;
        }

        return 0;
}