[fpc-pascal] fpSelect() with very small timeout?

[Graeme Geldenhuys]

Hi,

Below is some code I use in fpGUI-X11's main event loop. When I played
around with multithreading, I wrote a simple application, created 4
threads that each update there own ProgressBar.  I noticed that if I
don't move the mouse, the ProgressBar gets updated slowly. And when I
move the mouse over the form, the updates seem more smooth and
frequent. The default timeout for fpSelect was 1000ms.  I decreased
that to 50ms and now all GUI updates from the 4 threads are smooth.
With or without moving the mouse. CPU load also doesn't seem to be
affected - it's still between 0-1% load.

Is there any downsides I don't know about when using fpSelect() with
such a small timeout?

begin
  xfd := XConnectionNumber(display);
  XFlush(display);

  needToWait := True;
  if XPending(display) > 0 then // We have a X message to process
  begin
    XNextEvent(display, @ev);
    needToWait := False;
  end;

  if needToWait then  // No X messages to process (we are idle). So do
a timeout wait
  begin
    if Assigned(FOnIdle) then
      OnIdle(self);
    fpFD_ZERO(rfds);
    fpFD_SET(xfd, rfds);
    r := fpSelect(xfd + 1, @rfds, nil, nil, 50);    // 50ms timeout
    if r <> 0 then  // We got a X event or the timeout happened
      XNextEvent(display, @ev)
    else
      Exit; // nothing further to do here!
  end;

[... if we get here, we have X events to handle....]
end;


Regards,
  - Graeme -


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