  void queue(utime_t release, Message *m) {
    Mutex::Locker l(delay_lock);
    delay_queue.push_back(make_pair(release, m));
    delay_cond.Signal();
  }
  void queue(utime_t release, Message *m) {
    Mutex::Locker l(delay_lock);
    delay_queue.push_back(make_pair(release, m));
    delay_cond.Signal();
  }