static ItIt<Pair<S, Int>> returnCodesOfMultipleServers_parallel_iterator(int timeout, S... servers) {
  ret returnCodesOfMultipleServers_parallel_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<Pair<S, Int>> results = synchroList();
  
  // Fire up the threads (with timeouts)
  
  for (fS server : servers)
    thread "Server Check" {
      results.add(pair(server, returnCodeHttpHEADWithTimeout(timeout, server)));
      syncIncIntVar(counter);
    }
    
  // Make iterator delivering results as they come in
  ret iteratorFromFunction(new F0<Pair<S, Int>>() {
    int n = 0;
    
    public Pair<S, Int> get() {
      if (n >= l(servers)) null;
      waitForVarToChange(counter, n);
      ret results.get(n++);
    }
  });
}

Began life as a copy of #1018967