https://groups.google.com/a/dartlang.org/forum/#!topic/misc/SKJxKYdYljI

momdad.dart

import 'dart:async';

Stopwatch mom = new Stopwatch();
Stopwatch dad = new Stopwatch();
Duration dur = new Duration(milliseconds: 400);

Future mymom() async {
  if(mom.elapsed > dur){
    print('mom cooks');
    mom.reset();
  }
  mymom();
}

Future mydad() async {
  if(dad.elapsed > dur){
    print('dad works');
    dad.reset();
  }
  mydad();
}

main() {
  mom.start();
  dad.start();

  mymom();
  mydad();

  print('end of main');
}

$ dart --version  # Dart VM version: 1.8.0-dev.4.0 (Wed Nov 12 01:25:30 2014) on "linux_x64"
$ dart -c --enable-async momdad.dart 
# end of main
# mom cooks
# dad works
# mom cooks
# dad works
# ...