[fpc-pascal] TFPTimer does not fire, why?

[Michael Van Canneyt]

On Mon, 7 Sep 2020, Bo Berglund via fpc-pascal wrote:

> Ì have a problem using TFpTimer on Linux (FPC 3.0.4, Lazarus 2.0.8 on
> Raspbian).
> 
> The application is a small GUI test app where I have added a timer in
> order to update the display with incoming data.
> So I have it set up like this:
> 
> {$mode Delphi}
> interface
> uses
>  ...
>  fptimer,
>  ...
> type
>
>  TfrmMain = class(TForm)
>  ...
>  private
>    FTimCheckInputs: TFpTimer;
>  ...
>    procedure OnTimCheckInputs(Sender: TObject);
>  ...
> 
> implementation
> 
> procedure TfrmMain.FormCreate(Sender: TObject);
> begin
>  ...
>  FTimCheckInputs := TFpTimer.Create(NIL);
>  FTimCheckInputs.OnTimer := OnTimCheckInputs;
>  FTimCheckInputs.Interval := 500; // 500 ms latency
>  ...
> end;
> 
> procedure TfrmMain.OnTimCheckInputs(Sender: TObject);
> begin
>  ShowInByte; //<== This is NEVER reached!
> end;
> 
> procedure TfrmMain.btnOpenComClick(Sender: TObject);
> begin
>  ...
>  if FRemote.OpenPort(edComPort.Text, StrToInt(cbxBaud.Text)) then
>  begin
>    ...
>    FTimCheckInputs.Enabled := true;
>  end
>  else
>  begin
>    ...
>    FTimCheckInputs.Enabled := false;
>  end;
> end;
> 
> procedure TfrmMain.FormClose(Sender: TObject; var CloseAction:
> TCloseAction);
> begin
>  FTimCheckInputs.Enabled := false;
>  FTimCheckInputs.Free;
>  ...
> end;
> 
> When I click the btnOpenCom button I get to the button event and the
> code reachers the line:
>
>  FTimCheckInputs.Enabled := true;
> 
> So presumably here the timer should start and fire after 500 ms as set
> up in the FormCreate procedure.
> But it never does! I do not get into this at all. I have put a
> breakpoint there but it never fires, whereas other breakpoints do fire
> so I can see that for example btnOpenComClick fires off properly and
> the timer should be enabled.
> 
> And before you ask, I *have* this at the beginning of the lpr file:
> uses
>  {$IFDEF UNIX}
>  cthreads,
>  {$ENDIF}
> 
> 
> Why does the FpTimer event not fire?

Do you call checksynchronize at regular intervals ? The default timer is
threaded, and the OnTimer event is called in the main thread. For this to
work, you need to call checksynchronize at regular intervals in your main
thread.

Michael.