Xbase++

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. Xbase++

LOCAL nSuccess
LOCAL oHttp
LOCAL nWaitMaxMs
LOCAL cDownloadUrl
LOCAL oTask
LOCAL nWasCanceled

nSuccess := 0

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

oHttp := CreateObject("Chilkat.Http")

//  Set some timeouts, in seconds:
oHttp:ConnectTimeout := 15
oHttp: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.
nWaitMaxMs := 2000

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

oTask := oHttp:DownloadAsync(cDownloadUrl, "qa_output/mono.msi")
oTask: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.
oTask:Wait(nWaitMaxMs)

//  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 1 if the task was in the "queued" or "running" state and was canceled or aborted. 
//  The method returns 0 if the task has any other status.
nWasCanceled := oTask:Cancel()
IF (nWasCanceled == 1)
    ? "The HTTP download took too long and was canceled."
ELSE
    //  Find out what happened.
    IF (oTask:StatusInt == 7)
        //  The task completed, which means the background thread's call to Download completed
        //  with success or failure.  Find out which...
        nSuccess := oTask:GetResultBool()
        IF (nSuccess == 1)
            ? "Download successful!"
        ELSE
            ? "Download failed prior to waitMaxMs..."
            ? oTask:ResultErrorText
        ENDIF

    ELSE
        //  The task must've been canceled or aborted by some other means..
        ? "Task did not complete.  Final status: " + oTask:Status
    ENDIF

ENDIF

oTask:destroy()

oHttp:destroy()