Cancellable Futures Example - by Simon Lightfoot :: #HumpdayQandA on 16th April 2025 :: https://www.youtube.com/watch?v=CgiIh96C2DI

humpday_2025-04-16_1.dart

// MIT License
//
// Copyright (c) 2025 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'dart:async';
import 'dart:io';

class CancelException implements Exception {}

class CancellableTask {
  final _completer = Completer();
  bool cancel = false;

  Future<void> get done => _completer.future;

  Future<void> _task() async {
    cancel = false;
    int count = 0;
    while (!cancel && count < 5) {
      await Future.delayed(const Duration(milliseconds: 1000));
      print('period ${count++}');
    }
    if (cancel) {
      throw CancelException();
    }
    print('exiting');
    _completer.complete();
  }

  Future<void> call() {
    _task();
    return _completer.future;
  }
}

Future<void> main() async {
  print('waiting');

  final task = CancellableTask();
  task();

  ProcessSignal.sigint
      .watch() //
      .first
      .then((_) {
    print('sigint received');
    return task.cancel = true;
  });

  print('done');
}

Future<String> longRunningOperation() async {
  await Future.delayed(Duration(seconds: 5));
  return 'Operation completed';
}