Parent task does not wait for child task to complete

Question

So here is my code

Task parent = Task.Run(() =>
{
    var result = new int[3];

    TaskFactory tf = new TaskFactory(TaskCreationOptions.Atta         


        

Answer 1

Please use the code as below:

static void RunParentTask()
    {
        Task<int[]> parent = Task.Factory.StartNew<int[]>(() =>
        {
            var results = new int[3];

            TaskFactory<int> factory = new TaskFactory<int>(TaskCreationOptions.AttachedToParent,
                                                            TaskContinuationOptions.ExecuteSynchronously);
            factory.StartNew(() => results[0] = 1);
            factory.StartNew(() => results[1] = 2);
            factory.StartNew(() => results[2] = 3);

            return results;
        });

        parent.Wait();

        foreach (var item in parent.Result)
        {
            Console.WriteLine(item);
        }
    }

Answer 2

In Task.Run's documentation, you'll find that it specifies

Its CreationOptions property value is TaskCreationOptions.DenyChildAttach.

So, even though you specify TaskCreationOptions.AttachedToParent, it is ignored.

Answer 3

This behaviour is due to your use of the Task.Run method, which forbids child tasks from being attached to the parent:

The Run method is a simpler alternative to the StartNew method. It creates a task [whose] CreationOptions property value is TaskCreationOptions.DenyChildAttach.

To resolve, simply change your first line from

Task<int[]> parent = Task.Run(() =>

to

Task<int[]> parent = Task.Factory.StartNew(() =>