Question

Every variation on the following code that I try doesn’t work – whether DoSomething() : void and is called as written, or DoSomething() : Task and is called with TaskEx.RunEx(), some attempt involving .GetAwaiter().GetResult(). Errors seen include: "Start may not be called on a task with null action", "RunSynchronously may not be called on a task unbound to a delegate", and "The task has not yet completed".

class Program
{
    static void Main(string[] args) // Starting from a non-async method
    {
        DoSomething();

        Console.WriteLine("Press any key to quit.");
        Console.ReadKey();
    }

    static async void DoSomething()
    {
        Console.WriteLine("Starting DoSomething ...");

        var x = await PrepareAwaitable(1);

        Console.WriteLine("::" + x);

        var y = await PrepareAwaitable(2);

        Console.WriteLine("::" + y);
    }

    static Task<string> PrepareAwaitable(int id)
    {
        return new Task<string>(() =>
        {
            return "Howdy " + id.ToString();
        });
    }
}

Output:

Starting DoSomething …

Press any key to quit.

PrepareAwaitable‘s Task‘s Action will be more complicated later. When this action completes, however long that takes, I would expect the Task (or other Framework mechanisms) to resume by assigning "Howdy ..." to x, and then later to y. What I REALLY want to do is intercept the awaited objects, process them, and at some later time that I control, resume to the continuation with a result (x and y). But I haven’t been getting very far on that big step, so I’m trying to start smaller.

Answer 1

The tasks you returned haven’t started yet (i.e., they’re “cold” tasks); try replacing the PrepareAwaitable code with the following:

static Task<string> PrepareAwaitable(int x)
{
    return Task.Factory.StartNew<string>(() =>
    {
        return "Howdy " + x.ToString();
    });
}