Lianja

Cancel Async Task if not Completed after a Max Time

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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. Lianja

llSuccess = .F.

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

loHttp = createobject("CkHttp")

// Set some timeouts, in seconds:
loHttp.ConnectTimeout = 15
loHttp.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.
lnWaitMaxMs = 2000

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

loTask = loHttp.DownloadAsync(lcDownloadUrl,"qa_output/mono.msi")
loTask.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.
loTask.Wait(lnWaitMaxMs)

// 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 .T. if the task was in the "queued" or "running" state and was canceled or aborted. 
// The method returns .F. if the task has any other status.
llWasCanceled = loTask.Cancel()
if (llWasCanceled = .T.) then
    ? "The HTTP download took too long and was canceled."
else
    // Find out what happened.
    if (loTask.StatusInt = 7) then
        // The task completed, which means the background thread's call to Download completed
        // with success or failure.  Find out which...
        llSuccess = loTask.GetResultBool()
        if (llSuccess = .T.) then
            ? "Download successful!"
        else
            ? "Download failed prior to waitMaxMs..."
            ? loTask.ResultErrorText
        endif

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

endif

release loTask


release loHttp