Async Task.WhenAll with timeout

Question

Is there a way in the new async dotnet 4.5 library to set a timeout on the Task.WhenAll method. I want to fetch several sources and stop after say 5 seconds and

Answer 1

What you describe seems like a very common demand however I could not find anywhere an example of this. And I searched a lot... I finally created the following:

TimeSpan timeout = TimeSpan.FromSeconds(5.0);

Task[] tasksOfTasks =
{
    Task.WhenAny(SomeTaskAsync("a"), Task.Delay(timeout)),
    Task.WhenAny(SomeTaskAsync("b"), Task.Delay(timeout)),
    Task.WhenAny(SomeTaskAsync("c"), Task.Delay(timeout))
};

Task[] completedTasks = await Task.WhenAll(tasksOfTasks);

List = completedTasks.OfType>().Select(task => task.Result).ToList();

I assume here a method SomeTaskAsync that returns Task.

From the members of completedTasks, only tasks of type MyResult are our own tasks that managed to beat the clock. Task.Delay returns a different type. This requires some compromise on typing, but still works beautifully and quite simple.

(The array can of course be built dynamically using a query + ToArray).

• Note that this implementation does not require SomeTaskAsync to receive a cancellation token.