Pascal (Lazarus/Delphi)

Async Task Chain

See more Async Examples

Demonstrates how to combine a sequence of asynchronous tasks into a single task chain to be run in a background thread. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.MailMan,
  Chilkat.Task,
  Chilkat.TaskChain,
  Chilkat.Email;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  mailman: TMailMan;
  numMessages: Integer;
  taskChain: TTaskChain;
  i: Integer;
  task: TTask;
  email: TEmail;
  numTasks: Integer;
  taskIdx: Integer;

begin
  success := False;

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

  success := False;

  mailman := TMailMan.Create;

  //  Set the POP3 server's hostname
  mailman.MailHost := 'pop.example.com';

  //  Set the POP3 login/password and any other requirements..
  mailman.PopUsername := 'myLogin';
  mailman.PopPassword := 'myPassword';
  mailman.PopSsl := True;
  mailman.MailPort := 995;

  //  Connect to the POP3 server:
  success := mailman.Pop3BeginSession();
  if (not success) then
    begin
      WriteLn(mailman.LastErrorText);
      Exit;
    end;

  //  Get the number of messages in the mailbox.
  numMessages := mailman.GetMailboxCount();
  if (numMessages = 0) then
    begin
      WriteLn('No email messages in the POP3 mailbox.');
      Exit;
    end;

  taskChain := TTaskChain.Create;

  //  Create async task objects to fetch each email message
  //  by its sequence number

  for i := 1 to numMessages do
    begin

      task := mailman.FetchByMsgnumAsync(i);
      if (mailman.LastMethodSuccess = False) then
        begin
          WriteLn(mailman.LastErrorText);
          Exit;
        end;

      //  Append each task to the task chain.
      success := taskChain.Append(task);
      if (not success) then
        begin
          WriteLn(taskChain.LastErrorText);
          Exit;
        end;

      task.Free;

    end;

  //  At this point, no tasks have actually started running.
  //  All we've done so far is to create tasks for the work that will be done
  //  when the task chain is run.

  //  Start the task chain running in a background thread.
  //  Each task is run one after the other (on the same background thread) until all tasks have completed.
  //  The task chain will stop at the first task that fails.
  taskChain.StopOnFailedTask := True;
  success := taskChain.Run();
  if (not success) then
    begin
      WriteLn(taskChain.LastErrorText);
      Exit;
    end;

  //  The application is now free to do anything else
  //  while the emails are being downloaded

  //  For this example, we'll simply sleep and periodically
  //  check to see if the taskchain if finished. 
  while taskChain.Finished <> True do
    begin

      //  Sleep 100 ms.
      taskChain.SleepMs(100);

    end;

  //  A finished task chain could be one that was canceled, aborted, or truly finished.  

  //  If the task chain "completed", then it ran to completion.  A "completed" task will
  //  have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
  //  been aborted or canceled:
  if (taskChain.StatusInt <> 7) then
    begin
      WriteLn('Task did not complete.');
      WriteLn('task chain status: ' + taskChain.Status);
      Exit;
    end;

  email := TEmail.Create;

  numTasks := taskChain.NumTasks;
  taskIdx := 0;

  while (taskIdx < numTasks) do
    begin

      task := taskChain.GetTask(taskIdx);

      //  Load the email object with email downloaded by this task.
      success := email.LoadTaskResult(task);
      if (not success) then
        begin
          WriteLn('Failed to load email object for task.');
        end
      else
        begin
          WriteLn(email.From + '; ' + email.Subject);
        end;

      task.Free;

      taskIdx := taskIdx + 1;
    end;



  mailman.Free;
  taskChain.Free;
  email.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.