void wait_for_async(SSL *s)
{
    /* On Windows select only works for sockets, so we simply don't wait  */
#ifndef OPENSSL_SYS_WINDOWS
    int width = 0;
    fd_set asyncfds;
    OSSL_ASYNC_FD *fds;
    size_t numfds;
    size_t i;

    if (!SSL_get_all_async_fds(s, NULL, &numfds))
        return;
    if (numfds == 0)
        return;
    fds = app_malloc(sizeof(OSSL_ASYNC_FD) * numfds, "allocate async fds");
    if (!SSL_get_all_async_fds(s, fds, &numfds)) {
        OPENSSL_free(fds);
        return;
    }

    FD_ZERO(&asyncfds);
    for (i = 0; i < numfds; i++) {
        if (width <= (int)fds[i])
            width = (int)fds[i] + 1;
        openssl_fdset((int)fds[i], &asyncfds);
    }
    select(width, (void *)&asyncfds, NULL, NULL, NULL);
    OPENSSL_free(fds);
#endif
}