DataFlex

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. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoHttp
    Integer iWaitMaxMs
    String sDownloadUrl
    Variant vTask
    Handle hoTask
    Boolean iWasCanceled
    String sTemp1
    Integer iTemp1

    Move False To iSuccess

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

    Get Create (RefClass(cComChilkatHttp)) To hoHttp
    If (Not(IsComObjectCreated(hoHttp))) Begin
        Send CreateComObject of hoHttp
    End

    // Set some timeouts, in seconds:
    Set ComConnectTimeout Of hoHttp To 15
    Set ComReadTimeout Of hoHttp To 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.
    Move 2000 To iWaitMaxMs

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

    Get ComDownloadAsync Of hoHttp sDownloadUrl "qa_output/mono.msi" To vTask
    If (IsComObject(vTask)) Begin
        Get Create (RefClass(cComChilkatTask)) To hoTask
        Set pvComObject Of hoTask To vTask
    End
    Get ComRun Of hoTask To iSuccess

    // 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.
    Get ComWait Of hoTask iWaitMaxMs To iSuccess

    // 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.
    Get ComCancel Of hoTask To iWasCanceled
    If (iWasCanceled = True) Begin
        Showln "The HTTP download took too long and was canceled."
    End
    Else Begin
        // Find out what happened.
        Get ComStatusInt Of hoTask To iTemp1
        If (iTemp1 = 7) Begin
            // The task completed, which means the background thread's call to Download completed
            // with success or failure.  Find out which...
            Get ComGetResultBool Of hoTask To iSuccess
            If (iSuccess = True) Begin
                Showln "Download successful!"
            End
            Else Begin
                Showln "Download failed prior to waitMaxMs..."
                Get ComResultErrorText Of hoTask To sTemp1
                Showln sTemp1
            End

        End
        Else Begin
            // The task must've been canceled or aborted by some other means..
            Get ComStatus Of hoTask To sTemp1
            Showln "Task did not complete.  Final status: " sTemp1
        End

    End

    Send Destroy of hoTask


End_Procedure