C#.Rihter.ParentTasks and TaskFactory

Example

        static void Main(string[] args)
        {
            Task<Int32[]> parent = new Task<Int32[]>(() =>
            {
                var results = new Int32[3];
                StartNewTask(results, 0, 1);
                StartNewTask(results, 1, 2);
                StartNewTask(results, 2, 3);
                return results;
            });

            parent.ContinueWith(parentTask => Array.ForEach(parentTask.Result, Console.WriteLine));

            parent.Start();
            Thread.Sleep(3000);
        }

        static void StartNewTask(Int32[] results, int index, int value)
        {
            new Task(() => results[index] = value, TaskCreationOptions.AttachedToParent).Start();
        }

output

1
2
3

TASK FACTORY

        static void Main(string[] args)
        {
            Task parent = new Task(() =>
            {
                var cts = new CancellationTokenSource();
                // create params for tasks in one place
                var tf = new TaskFactory<int>(
                    cts.Token,
                    TaskCreationOptions.AttachedToParent,
                    TaskContinuationOptions.ExecuteSynchronously,
                    TaskScheduler.Default
                );

                var childTasks = new[]
                {
                    tf.StartNew(() =>
                    {
                        Thread.Sleep(1000);
                        return 1;
                    }, cts.Token),
                    tf.StartNew(() =>
                    {
                        Thread.Sleep(1000);
                        return 2;
                    }, cts.Token),
                };

                // if at least one task will be faulted we exit all with cts.Cancel()
                foreach (var task in childTasks)
                {
                    task.ContinueWith(t => cts.Cancel(), TaskContinuationOptions.OnlyOnFaulted);
                }

                // process with results
                tf.ContinueWhenAll(
                    childTasks,
                    (completedTasks) => completedTasks.Max(t => t.Result
                    )).ContinueWith((t) => Console.WriteLine(("Result is " + t.Result)), cts.Token);
            });
            
            parent.Start();
            Thread.Sleep(5000);
        }
    }

Result is 2