Why won't TTimer work in OTL worker task?

I wanted to realize a repetitive task in an OmniThreadLibrary worker task, that runs in another thread. The task should be executed every 3 seconds, for example. Therefore I wrote a TOmniWorker descendant with an instance of TTimer as you can see below:

program Project14;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  Vcl.ExtCtrls,
  Vcl.Forms,
  OtlTaskControl;

type
  TMyTimerWorker = class(TOmniWorker)
  strict private
    FTimer: TTimer;
    procedure DoOnTimer(Sender: TObject);
  protected
    function Initialize: Boolean; override;
    procedure Cleanup; override;
  end;

{ TMyTimerWorker }

procedure TMyTimerWorker.Cleanup;
begin
  FTimer.Free;
  inherited;
end;

procedure TMyTimerWorker.DoOnTimer(Sender: TObject);
begin
  Beep;
end;

function TMyTimerWorker.Initialize: Boolean;
begin
  Result := inherited;
  if not Result then exit;

  FTimer := TTimer.Create(nil);
  FTimer.OnTimer  := DoOnTimer;
  FTimer.Interval := 3000;
  FTimer.Enabled  := True; // note: this isn't necessary, but is added to avoid hints that 'Enabled' might be 'False'
end;

var
  LTimerWorker: IOmniWorker;
begin
  try
    LTimerWorker := TMyTimerWorker.Create;
    CreateTask(LTimerWorker).Unobserved.Run;
    while True do
      Application.ProcessMessages;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

I set breakpoints in Initialize and DoOnTimer. Former executes well but latter won't be called at all. BTW: Cleanup isn't called neither, so the task is still running.

What am I doing wrong? Is it impossible to use a TTimer in an OTL task? If yes, why?

UPDATE: I found a workaround for TTimer () but why does TTimer approach not work?

Solution

You TTimer-based code doesn't work because TTimer uses windows messages to trigger the timer event and windows messages are not processed in an OTL worker by default.

Call .MsgWait before .Run and internal worker loop will use MsgWaitForMultipleObjects instead of WaitForMultipleObjects which will allow for message processing.

Saying that, you really should not use TTimer in background tasks because - as others have said - TTimer is not threadsafe.