svoid waitUntil(int interval, IF0<Bool> condition) {
  if (condition == null) ret;
  while (!condition.get()) sleep(interval);
}

sbool waitUntil(int interval, double timeout, IF0<Bool> condition) {
  if (condition == null) false;
  long start = sysNow();
  while (sysNow() < start+toMS(timeout))
    if (condition.get())
      true;
    else
      sleep(interval);
  false;
}