multitasking 4.1.0

Cooperative multitasking using asynchronous tasks and synchronization primitives, with the ability to safely cancel groups of nested tasks performing I/O wait or listen operations.

example/example.dart

import 'dart:async';

import 'package:http/http.dart';
import 'package:multitasking/multitasking.dart';

Future<void> main() async {
  final cts = CancellationTokenSource();
  final token = cts.token;
  final list = [
    (
      '3.11.1',
      'https://storage.googleapis.com/dart-archive/channels/stable/release/3.11.1/sdk/dartsdk-windows-x64-release.zip'
    ),
    (
      '3.10.9',
      'https://storage.googleapis.com/dart-archive/channels/stable/release/3.10.9/sdk/dartsdk-windows-x64-release.zip'
    )
  ];

  final tasks = <AnyTask>[];
  for (final element in list) {
    final url = Uri.parse(element.$2);
    final filename = element.$1;
    final task = _download(url, filename, token);
    tasks.add(task);
  }

  // User request to cancel
  Timer(Duration(seconds: 2), () {
    print('Canceling...');
    cts.cancel();
  });

  try {
    await Task.waitAll(tasks);
  } catch (e) {
    print('$e');
  }

  for (final task in tasks) {
    if (task.isCompleted) {
      final filename = await task;
      print('Done: $filename');
    }
  }
}

Task<String> _download(Uri uri, String filename, CancellationToken token) {
  return Task.run(() async {
    final bytes = <int>[];

    Task.onExit((task) {
      print('${task.toString()}: ${task.state.name}');
      _message('Downloaded: ${bytes.length}');
    });

    token.throwIfCanceled();
    final client = Client();
    final abortTrigger = Completer<void>();

    Future<void> get() async {
      final request =
          AbortableRequest('GET', uri, abortTrigger: abortTrigger.future);
      final StreamedResponse response;
      try {
        response = await client.send(request);
      } on RequestAbortedException {
        throw TaskCanceledException();
      }

      try {
        await response.stream.listen(bytes.addAll).asFuture<void>();
      } on RequestAbortedException {
        throw TaskCanceledException();
      }
    }

    await token.runCancelable(abortTrigger.complete, get);

    // Save file to disk
    await Future<void>.delayed(Duration(seconds: 1));
    return filename;
  });
}

void _message(String text) {
  final task = Task.current.name ?? '${Task.current}';
  print('$task: $text');
}