Why won't TTimer work in OTL worker task? - delphi

Question

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?

Answer 1

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.