Delphi DLL

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. Delphi DLL

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
mailman: HCkMailMan;
numMessages: Integer;
taskChain: HCkTaskChain;
i: Integer;
task: HCkTask;
email: HCkEmail;
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 := CkMailMan_Create();

// Set the POP3 server's hostname
CkMailMan_putMailHost(mailman,'pop.example.com');

// Set the POP3 login/password and any other requirements..
CkMailMan_putPopUsername(mailman,'myLogin');
CkMailMan_putPopPassword(mailman,'myPassword');
CkMailMan_putPopSsl(mailman,True);
CkMailMan_putMailPort(mailman,995);

// Connect to the POP3 server:
success := CkMailMan_Pop3BeginSession(mailman);
if (not success) then
  begin
    Memo1.Lines.Add(CkMailMan__lastErrorText(mailman));
    Exit;
  end;

// Get the number of messages in the mailbox.
numMessages := CkMailMan_GetMailboxCount(mailman);
if (numMessages = 0) then
  begin
    Memo1.Lines.Add('No email messages in the POP3 mailbox.');
    Exit;
  end;

taskChain := CkTaskChain_Create();

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

for i := 1 to numMessages do
  begin

    task := CkMailMan_FetchByMsgnumAsync(mailman,i);
    if (CkMailMan_getLastMethodSuccess(mailman) = False) then
      begin
        Memo1.Lines.Add(CkMailMan__lastErrorText(mailman));
        Exit;
      end;

    // Append each task to the task chain.
    success := CkTaskChain_Append(taskChain,task);
    if (not success) then
      begin
        Memo1.Lines.Add(CkTaskChain__lastErrorText(taskChain));
        Exit;
      end;

    CkTask_Dispose(task);

  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.
CkTaskChain_putStopOnFailedTask(taskChain,True);
success := CkTaskChain_Run(taskChain);
if (not success) then
  begin
    Memo1.Lines.Add(CkTaskChain__lastErrorText(taskChain));
    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 CkTaskChain_getFinished(taskChain) <> True do
  begin

    // Sleep 100 ms.
    CkTaskChain_SleepMs(taskChain,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 (CkTaskChain_getStatusInt(taskChain) <> 7) then
  begin
    Memo1.Lines.Add('Task did not complete.');
    Memo1.Lines.Add('task chain status: ' + CkTaskChain__status(taskChain));
    Exit;
  end;

email := CkEmail_Create();

numTasks := CkTaskChain_getNumTasks(taskChain);
taskIdx := 0;

while (taskIdx < numTasks) do
  begin

    task := CkTaskChain_GetTask(taskChain,taskIdx);

    // Load the email object with email downloaded by this task.
    success := CkEmail_LoadTaskResult(email,task);
    if (not success) then
      begin
        Memo1.Lines.Add('Failed to load email object for task.');
      end
    else
      begin
        Memo1.Lines.Add(CkEmail__from(email) + '; ' + CkEmail__subject(email));
      end;

    CkTask_Dispose(task);

    taskIdx := taskIdx + 1;
  end;

CkMailMan_Dispose(mailman);
CkTaskChain_Dispose(taskChain);
CkEmail_Dispose(email);

end;