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(Delphi DLL) Cancel Async Task if not Completed after a Max Time

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.

Chilkat for Delphi Downloads

Chilkat non-ActiveX DLL for Delphi

Chilkat ActiveX DLL for Delphi

* The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Task, Http;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
http: HCkHttp;
waitMaxMs: Integer;
downloadUrl: PWideChar;
task: HCkTask;
wasCanceled: Boolean;

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

http := CkHttp_Create();

//  Set some timeouts, in seconds:
CkHttp_putConnectTimeout(http,15);
CkHttp_putReadTimeout(http,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.
waitMaxMs := 2000;

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

task := CkHttp_DownloadAsync(http,downloadUrl,'qa_output/mono.msi');
CkTask_Run(task);

//  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.
CkTask_Wait(task,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.
wasCanceled := CkTask_Cancel(task);
if (wasCanceled = True) then
  begin
    Memo1.Lines.Add('The HTTP download took too long and was canceled.');
  end
else
  begin
    //  Find out what happened.
    if (CkTask_getStatusInt(task) = 7) then
      begin
        //  The task completed, which means the background thread's call to Download completed
        //  with success or failure.  Find out which...
        success := CkTask_GetResultBool(task);
        if (success = True) then
          begin
            Memo1.Lines.Add('Download successful!');
          end
        else
          begin
            Memo1.Lines.Add('Download failed prior to waitMaxMs...');
            Memo1.Lines.Add(CkTask__resultErrorText(task));
          end;
      end
    else
      begin
        //  The task must've been canceled or aborted by some other means..
        Memo1.Lines.Add('Task did not complete.  Final status: ' + CkTask__status(task));
      end;
  end;

CkTask_Dispose(task);

CkHttp_Dispose(http);

end;

 

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