.NET 4.0's Task class - Promise interface?

Question

Is there a promise interface for the Task class like jQuery's deferred's promise method?

Answer 1

The TPL, and the Task class, are very different than jQuery's promise.

A Task is actually effectively more like the original action. If you wanted to have something run when the task completed, you'd use a continuation on the Task. This would effectively look more like:

Task someTask = RunMethodAsync();
someTask.ContinueWith( t =>
{
   // This runs after the task completes, similar to how promise() would work
});

If you want to continue on multiple tasks, you can use Task.Factory.ContinueWhenAll or Task.Factory.ContinueWhenAny to make continuations that works on multiple tasks.

Answer 2

It seems like you're looking for TaskCompletionSource:

var tcs = new TaskCompletionSource<Args>(); 

var obj = new SomeApi();

// will get raised, when the work is done
obj.Done += (args) => 
{
    // this will notify the caller 
    // of the SomeApiWrapper that 
    // the task just completed
    tcs.SetResult(args);
}

// start the work
obj.Do();

return tcs.Task;

The code is taken from here: When should TaskCompletionSource<T> be used?

Answer 3

That sounds like a continuation, so use .ContinueWith(callback); or in C# 5.0, simply await, i.e.

var task = /*...*/
var result = await task;
// everything here happens later on, when it is completed
// (assuming it isn't already)

different API, but I think it does what you are asking (a little hard to be sure... I'm not entirely sure I understand the question)