Parallel streams

main.dart

void main() async {
  upload(1).listen((event) {});
  await Future.delayed(Duration(seconds: 1));
  upload(2).listen((event) {});
  await Future.delayed(Duration(seconds: 1));
  upload(3).listen((event) {});
  await Future.delayed(Duration(seconds: 1));
  upload(4).listen((event) {});
  await Future.delayed(Duration(seconds: 1));
  upload(5).listen((event) {});
  await Future.delayed(Duration(seconds: 1));
  upload(6).listen((event) {});
}

Stream<void> upload(int order) async* {
  for (var i = 0; i < 1000; i++) {
    print('$order order $i before');
    await Future.delayed(Duration(seconds: 1));
    print('$order order $i after');
  }
}