If my interface must return Task what is the best way to have a no-operation implementation?

In the code below, due to the interface, the class LazyBar must return a task from its method (and for argument's sake can't be changed). If LazyBars implementation is unusual in that it happens to run quickly and synchronously - what is the best way to return a No-Operation task from the method?

I have gone with Task.Delay(0) below, however I would like to know if this has any performance side-effects if the function is called a lot (for argument's sake, say hundreds of times a second):

• Does this syntactic sugar un-wind to something big?

• Does it start clogging up my application's thread pool?

• Is the compiler cleaver enough to deal with Delay(0) differently?

• Would return Task.Run(() => { }); be any different?

Is there a better way?

```
using System.Threading.Tasks;

namespace MyAsyncTest
{
internal interface IFooFace
{
Task WillBeLongRunningAsyncInTheMajorityOfImplementations();
}

///
/// An implementation, that unlike most cases, will not have a long-running
/// operation in 'WillBeLongRunningAsyncInTheMajorityOfImplementations'
///
internal class LazyBar : IFooFace
{
#region IFooFace Members

public Task WillBeLongRunningAsyncInTheMajorityOfImplementations()
{
// First, do something really quick
var x = 1;

// Can't return 'null' here! Does 'Task.Delay(0)' have any performance considerations?
// Is it a real no-op, or if I call this a lot, will it adversely affect the
// underlying thread-pool? Better way?
return Task.Delay(0);

// Any different?
// return Task.Run(() => { });

// If my task returned something, I would do:
// return Task.FromResult(12345);
}

#endregion
}

internal class Program
{
private static void Main(string[] args)
{
Test();
}

private static async void Test()

Today, I would recommend using Task.CompletedTask to accomplish this.

Pre .net 4.6:

Using Task.FromResult(0) or Task.FromResult(null) will incur less overhead than creating a Task with a no-op expression. When creating a Task with a result pre-determined, there is no scheduling overhead involved.

Stack Overflow Q#13127177, score: 802