have a question to ask in function[ngx_http_upstream_check_recv_handler]

[liuhaicheng]

if (peer->state != NGX_HTTP_CHECK_SEND_DONE) {

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        goto check_recv_fail;
    }

    return;
}

why need to add this code