static ItIt<Pair<S, Int>> returnCodesOfMultipleServers_parallel_iterator(int timeout, S... servers) {
  ret returnCodesOfMultipleServers_iterator(timeout, asList(servers));
}

static ItIt<Pair<S, Int>> returnCodesOfMultipleServers_parallel_iterator(final int timeout, final Collection<S> servers) {
  final Var<Int> counter = new(0);
  final L<S> results = synchroList();
  for (fS server : servers)
    thread "Server Check" {
      results.add(returnCodeHttpHEADWithTimeout(timeout, server));
      syncIncIntVar(counter);
    }
  ret iteratorFromFunction(new VF1<Pair<S, Int>>() {
    int n = 0;
    
    public Pair<S, Int> get() {
      if (n >= l(servers)) null;
      waitForVarToChange(counter, n);
      ret results.get(n++);
    }
  });
}