cancel.dart

import 'dart:async';

/// This examples starts nested asynchronous operations
/// and cancels _everything_ still pending after 1 second.
///
/// Then, each individual operation can perform custom clean-up
/// inside their `finally` block.

const timeoutDuration = Duration(seconds: 2, milliseconds: 100);

void main() async {
  example() //
      .timeout(timeoutDuration)
      .first
      .then(
        (_) => print('finished'),
        onError: (_) => print('timed out'),
      );
}

Stream<void> example() async* {
  var completed = false;
  try {
    await delayedPrint('hello').first;
    print('did print hello');
    await Future.delayed(Duration(seconds: 1));
    print('did delay');
    await delayedPrint('world').first;
    print('did print world');
    completed = true;
  } finally {
    completed ? print('completed example()') : print('cancelled example()');
  }
}

Stream<void> delayedPrint(String msg) async* {
  bool completed = false;
  try {
    await Future.delayed(Duration(seconds: 1));
    print(msg);
    completed = true;
  } finally {
    completed ? print('completed $msg') : print('cancelled $msg');
  }
}