Making sure async tasks complete before vb.net application terminates

Question

I'm creating a vb.net desktop application. This application includes some asynchronous functions. When the user closes the application via the red X in the upper-right corner, there is some logic to possibly run one or more of these async functions. The problem is, the program terminates before they are complete. I figured using "Await" in my call would do that, but apparently not.

I found this thread that talks about using ManualResetEvent, but I'm having trouble understanding all of it, especially since the question is in the context of a console app, and the MSDN documentation the answer links to is about specifying threads, not simply using async tasks. As an attempt at using it anyway, I tried adding this to my main form:

Public resetEvent As ManualResetEvent = New ManualResetEvent(False)

And immediately after the call to one of these functions, I added this (quote includes the call):

Await activeCount.SerializeAsync(activeCount)
resetEvent.WaitOne()

And at the end of my async function itself, before returning the Task, added this:

frmMain.resetEvent.Set()

I don't think I'm using that right, though. The program still terminates before it's complete anyway.

Even before that, I figured the best place for such a thing would be in ApplicationEvents MyApplication_Shutdown, but I'm not sure how to know if such a function is still running at that point.

So what is the best way to make sure all my async functions complete before the application terminates in this situation?

Thank you!

---

UPDATE AFTER ACCEPTED ANSWER:

Though F0r3v3r-A-N00b's answer worked, I realized I need to use a dialog in certain cases. I couldn't call that within the background worker because the dialog is on the GUI thread, not the background thread. I tried moving things around so I'd call the dialog first, then make the background worker and all that, but for whatever reason I couldn't get it to work.

Long story short, I got around it by simply making a synchronous version of my functions, and so I could say 'if the user terminated the program and I need to call any of these functions before closing, call the synchronous versions instead'. That works. Thanks!

Answer 1

Try this. Create a new project. Add 1 label and backgroundworker to your form. Paste this in your form's code area:

Public Class Form1
Dim taskCompleted As Boolean = False
Dim taskIsrunning As Boolean = False

Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    Threading.Thread.Sleep(5000)
End Sub






Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
    taskCompleted = True
    taskIsRunning = False
    Label1.Text = "Background task completed."
    Me.Close()
End Sub






Private Sub Form1_FormClosing(sender As Object, e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
    If taskIsRunning Then
       e.Cancel = True
       Exit Sub
    End If

    If Not taskCompleted Then
        taskIsRunning = True
        Label1.Text = "Starting background task."
        BackgroundWorker1.RunWorkerAsync()
        Label1.Text = "Background task is running."
        e.Cancel = True
    End If
End Sub
End Class