Waiting for Unwrap ()

Question

For a method such as

public async Task<Task> ActionAsync() { ... } 

What's the difference between

 await await ActionAsync(); 

and

 await ActionAsync().Unwrap(); 

If there are any.

Answer 1

Unwrap() creates a new instance of the task that represents the entire operation for each call. Unlike await task created in this way is different from the original internal task. See Unwrap () docs and view the following code:

 private async static Task Foo() { Task<Task<int>> barMarker = Bar(); Task<int> awaitedMarker = await barMarker; Task<int> unwrappedMarker = barMarker.Unwrap(); Console.WriteLine(Object.ReferenceEquals(originalMarker, awaitedMarker)); Console.WriteLine(Object.ReferenceEquals(originalMarker, unwrappedMarker)); } private static Task<int> originalMarker; private static Task<Task<int>> Bar() { originalMarker = Task.Run(() => 1);; return originalMarker.ContinueWith((m) => m); } 

Exit:

 True False 

Update with .NET 4.5.1 Performance Test:. I tested both versions, and it turns out that the double await version is better in terms of memory usage. I used the Visual Studio 2013 memory profiler. The test includes 100,000 calls of each version.

64:

 ╔══════════════════╦═══════════════════════╦═════════════════╗ ║ Version ║ Inclusive Allocations ║ Inclusive Bytes ║ ╠══════════════════╬═══════════════════════╬═════════════════╣ ║ await await ║ 761 ║ 30568 ║ ║ await + Unwrap() ║ 100633 ║ 8025408 ║ ╚══════════════════╩═══════════════════════╩═════════════════╝ 

x86:

 ╔══════════════════╦═══════════════════════╦═════════════════╗ ║ Version ║ Inclusive Allocations ║ Inclusive Bytes ║ ╠══════════════════╬═══════════════════════╬═════════════════╣ ║ await await ║ 683 ║ 16943 ║ ║ await + Unwrap() ║ 100481 ║ 4809732 ║ ╚══════════════════╩═══════════════════════╩═════════════════╝ 

Answer 2

There will be no functional difference.