VB.NET

Cancel Async Task if not Completed after a Max Time

See more Async Examples

Demonstrates how to wait a maximum amount of time for an asynchronous task to completed. If not completed in the allotted amount of time, the task is cancelled. VB.NET

Dim success As Boolean = False

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim http As New Chilkat.Http

' Set some timeouts, in seconds:
http.ConnectTimeout = 15
http.ReadTimeout = 15

' Wait a max time of 2 seconds for the task.
' In this example, it's an unreasonably small amount of time,
' which means the task will get cancelled.
Dim waitMaxMs As Integer = 2000

' We're just going to download for 2 seconds and then cancel.
' Substitute your own URL with a large enough file for testing..
Dim downloadUrl As String = "http://download.mono-project.com/archive/4.6.1/windows-installer/mono-4.6.1.5-gtksharp-2.12.38-win32-0.msi"

Dim task As Chilkat.Task = http.DownloadAsync(downloadUrl,"qa_output/mono.msi")
task.Run()

' Wait a maximum of waitMaxMs for the task (i.e. the HTTP download) to complete.
' The Wait method returns when the task has been canceled, aborted, or completed, or when the max allotted time has passed.
task.Wait(waitMaxMs)

' At this point, the download may or may not have completed.  
' Rather than checking the Task status, we can call task.Cancel because
' if the Task is no longer running (because it already completed, was canceled or aborted), then the 
' call to Cancel is a NO-OP (meaning it does nothing and the Task's status is unaffected).
' Also, task.Cancel returns True if the task was in the "queued" or "running" state and was canceled or aborted. 
' The method returns False if the task has any other status.
Dim wasCanceled As Boolean = task.Cancel()
If (wasCanceled = True) Then
    Debug.WriteLine("The HTTP download took too long and was canceled.")
Else
    ' Find out what happened.
    If (task.StatusInt = 7) Then
        ' The task completed, which means the background thread's call to Download completed
        ' with success or failure.  Find out which...
        success = task.GetResultBool()
        If (success = True) Then
            Debug.WriteLine("Download successful!")
        Else
            Debug.WriteLine("Download failed prior to waitMaxMs...")
            Debug.WriteLine(task.ResultErrorText)
        End If

    Else
        ' The task must've been canceled or aborted by some other means..
        Debug.WriteLine("Task did not complete.  Final status: " & task.Status)
    End If

End If