struct kevent events_to_monitor;
    struct kevent event_data;
    struct timespec timeout;
    unsigned int vnode_events;
    void *data = (void *) _filename.c_str();
    int kq;
    int event_fd;

event_fd = open(_filename.c_str(), O_EVTONLY);
if (event_fd <=0) {
    fprintf(stderr, "The file %s could not be opened for monitoring.  Error was %s.n", _filename.c_str(), strerror(errno));
    exit(-1);
}

    /* Open a kernel queue. */
    if ((kq = kqueue()) < 0) {
        fprintf(stderr, "Could not open kernel queue.  Error was %s.n", strerror(errno));
    }

    timeout.tv_sec = 0;        // 0 seconds
    timeout.tv_nsec = 500000000;    // 500 milliseconds
    vnode_events = NOTE_DELETE | NOTE_EXTEND | NOTE_WRITE | NOTE_ATTRIB;
    EV_SET( &events_to_monitor, event_fd, EVFILT_VNODE, EV_ADD | EV_CLEAR, vnode_events, 0, NULL);

    while (1) {
        int event_count = kevent(kq, &events_to_monitor, NUM_EVENT_SLOTS, &event_data, 1, NULL);
        if ((event_count < 0) || (event_data.flags == EV_ERROR)) {
            /* An error occurred. */
            fprintf(stderr, "An error occurred (event count %d).  The error was %s.n", event_count, strerror(errno));
            break;
        }
        if (event_count) {
            printf("Event %" PRIdPTR " occurred.  Filter %d, flags %d, filter data %" PRIdPTR ", path %sn",
                   event_data.ident,
                   event_data.filter,
                   event_data.flags,
                   event_data.data,
                   (char *) event_data.udata);
        } else {
            printf("No event.n");
        }

        /* Reset the timeout.  In case of a signal interrruption, the
           values may change. */
        timeout.tv_sec = 0;        // 0 seconds
        timeout.tv_nsec = 500000000;    // 500 milliseconds
    }