Question

I’m trying out the new async and await keywords using VS2012RC and .NET 4.5 with just a simple delegate that returns a string, which works fine when I run a single one:

string message = await Task.Run(() => { return "something"; });

but when I try WhenAny:

string message = await Task.WhenAny(new Task<string>(() => { return "something"; })).Result;

it just never completes…why?

I’ve been watching a video by Steve Sanderson from TechDays 2012 Netherlands which makes this look really easy: http://channel9.msdn.com/Events/TechDays/Techdays-2012-the-Netherlands/2287

Answer 1

When you create a Task using its constructor, it’s not started yet. You have to call Start() to actually start it.

I think you should to use Task.Run() in your second version too, which returns you a Task that’s already started.

Also, it’s a bad idea to mix asynchronous waiting (await) with synchronous waiting (Result or Wait()), because it can lead to a deadlock.

So, I would write your code as:

var task = await Task.WhenAny(Task.Run(() => "something"));
string message = await task;

(Of course, there is no reason to use Task.WhenAny() when you have only one Task, but I’m assuming this is just an example.)