main.dart

void main(List<String> args) {
  awaitSerial(); //🚶‍♂️  slow running
  awaitParallel(); //🚴‍♂️ fast running
}

Future<int> getTotalClients() => Future.delayed(const Duration(seconds: 2), () => 1500000);

Future<int> getTotalUsers() => Future.delayed(const Duration(seconds: 2), () => 1500000);

Future<void> awaitSerial() async {
  final startTime = Stopwatch()..start();
  final totalUsers = await getTotalUsers();
  final totalClients = await getTotalClients();
  startTime.stop();
  print(
    'awaitSerial: ${startTime.elapsed.inSeconds}, total: ${totalUsers + totalClients}',
  );
}

Future<void> awaitParallel() async {
  final startTime = Stopwatch()..start();
  final getTotals = await Future.wait([
    getTotalClients(),
    getTotalUsers(),
  ]);
  startTime.stop();
  print(
    'awaitParallel: ${startTime.elapsed.inSeconds}, total: ${getTotals.fold<int>(0, (previousValue, element) => previousValue + element)}',
  );
}