CODEWITHSUNDEEP
vb.netasynchronousasync-awaittask
Fox
Fox

Reputation: 584

Is it possible to await the calling task?

Is there a way to await the calling task?

Async Function DoStuff() As Task
    StartDoingOtherStuff()

    ' Doing stuff
End Function

Async Function StartDoingOtherStuff() As Task
    ' Doing stuff

    Await callingTask

    ' Finish up
End Function

Note: I want to paralize the task, because it involves uploading a file to multiple destinations. But I want to await the calling task, to delete the file after all uploads are complete.

Upvotes: 0

Views: 454

Answers (1)

Visual Vincent
Visual Vincent

Reputation: 18310

Based on usr's answer to Get the current Task instance in an async method body, you can do this:

Private Async Function DoStuff() As Task
    'Capture the resulting task in a variable.
    Dim t As Task = (
        Async Function() As Task
            Console.WriteLine("DoStuff()")

            'First await. Required in order to return the task to 't'.
            Await Task.Delay(1)

            'Disable warnings:
            '    "Because this call is not awaited (...)"
            '    "Variable 't' is used before it has been assigned a value (...)"

#Disable Warning BC42358, BC42104

            'Call other method.
            DoOtherStuff(t)

#Enable Warning BC42358, BC42104

            'Simulate process.
            Await Task.Delay(3000)
        End Function
    ).Invoke()

    'Await if needed.
    Await t
End Function

Private Async Function DoOtherStuff(ByVal ParentTask As Task) As Task
    Console.WriteLine("DoOtherStuff()")

    'Await parent task.
    Await ParentTask

    Console.WriteLine("DoStuff() finished!")
End Function

By using a lambda expression you can capture the current task and then pass it to itself. Await Task.Delay(1) is required in order for the async method to return its task so that it can be set to the variable. However, you can remove it if you already have another await before DoOtherStuff() is called.

Upvotes: 1

Related Questions