The asynchronous controller method does not return


This code hangs (does not return a response) when I make a request to it:

public class MyController : ApiController
    public async Task<IQueryable<int>> Get()
        return await new Task<IQueryable<int>>(() => new List<int>().AsQueryable());

But this method works fine:

public IQueryable<int> Get()
    return new List<int>().AsQueryable();

What fundamental knowledge am I missing??!

As the other answer noted, the reason your controller is not finishing is because the task is not started. However, using Task.Start, Task.Factory.StartNew, or Task.Run is not a good solution on ASP.NET.

The entire point of using async/await on ASP.NET is to free up a thread. However, if you await a task that is started via Start/StartNew/Run, then you're freeing up one thread by taking up another thread from the same thread pool. In this case, you not only lose all the benefits of async/await, but you actually decrease your scalability by regularly throwing off the ASP.NET thread pool heuristics.

There are two types of tasks, as I describe on my blog: Delegate Tasks (which represent some work executed on a thread) and Promise Tasks (which represent an event). You should avoid Delegate Tasks on ASP.NET, including any tasks that are "started" (Start/StartNew/Run).

Since you're returning an IQueryable<T>, I'm assuming that your actual underlying operation is a database query. If you're using EF6, then you have full support for asynchronous queries, which are properly implemented with Promise Tasks.