How can I cancel Task.WhenAll?

Question

Currenly using the following code to wait for a collection of tasks to complete. However, I now have a situation where I want to be able to cancel/abort the WhenAll call, v

Answer 1

More elegant from my opinion :

await Task.Run(()=> Task.WaitAll(myArrayOfTasks), theCancellationToken);

Answer 2

Dim tcs as new TaskCompletionSource(Of Object)()
Await Tasks.Task.WhenAny(Tasks.Task.WhenAll(TaskCollection), tcs)

To cancel, call tcs.SetResult(Nothing). This will fire your Task.WhenAny.

Answer 3

You can also await a delay:

await Task.WhenAny(Task.WhenAll(tasks), Task.Delay(1000));

Answer 4

Use TaskCompletionSource<T> to create a task for some asynchronous condition that does not already have an asynchronous API. Use CancellationToken.Register to hook the modern CancellationToken-based cancellation system into another cancellation system. Your solution just needs to combine these two.

I have a CancellationToken.AsTask() extension method in my AsyncEx library, but you can write your own as such:

<System.Runtime.CompilerServices.Extension> _
Public Shared Function AsTask(cancellationToken As CancellationToken) As Task
  Dim tcs = New TaskCompletionSource(Of Object)()
  cancellationToken.Register(Function() tcs.TrySetCanceled(), useSynchronizationContext := False)
  Return tcs.Task
End Function

Usage is as you expected:

Await Task.WhenAny(Task.WhenAll(taskCollection), cancellationToken.AsTask())