Re: [Flightgear-devel] FlightGear/Plib periodic stutter notes

[Melchior F. <mf...@ao...>]

* Durk Talsma -- Sunday 30 September 2007:
> Thirdly, there is a relation between execution time and listeners, 

Err ... Nasal listeners trigger Nasal code when the listened-to property
is written to. Executed code costs cpu cycles. Anyone surprised?

If listeners are used badly and trigger bad code, then this will, of
course, hurt the framerate. But that's not because listeners are bad.

The problem that I see in the Seneca is that several listeners are
used on properties that are written to in every frame, which make
no sense. That's a slow replacement for a simple Nasal loop.

If you turn on listener logging, then you see a continuous flood of
triggered listener code:

  $ fgfs --aircraft=SenecaII --log-level=debug 2>&1|grep listener
  ...
  setting listener #50 in $FG_ROOT/Aircraft/SenecaII/Nasal/SenecaII.nas, line 269
  setting listener #51 in $FG_ROOT/Nasal/aircraft.nas, line 216
  setting listener #52 in $FG_ROOT/Nasal/aircraft.nas, line 216
  setting listener #62 in $FG_ROOT/Aircraft/SenecaII/Nasal/SenecaII.nas, line 437
  setting listener #63 in $FG_ROOT/Aircraft/SenecaII/Nasal/SenecaII.nas, line 438
  setting listener #69 in $FG_ROOT/Aircraft/SenecaII/Nasal/hsi.nas, line 16
  setting listener #79 in $FG_ROOT/Aircraft/SenecaII/Nasal/NLG.nas, line 66
  setting listener #80 in $FG_ROOT/Aircraft/SenecaII/Nasal/NLG.nas, line 67
  ...
  trigger listener #50
  trigger listener #51
  trigger listener #52
  trigger listener #62
  trigger listener #63
  trigger listener #79
  trigger listener #80
  trigger listener #69
  ...

That's bad and the reason why I added listener logging. Listener should
only be used on nodes that only change occasionally, as I've said
numerous times. But I can't *force* people to use them correctly.  :-}

If you run the bo105 with turned on logging, you won't see a flood of
triggered listeners (unless you move the mouse, #21 and #22). You'll
only see them if some special "event" happens. Try that. It can't
cause any stuttering.

m.



BTW: the two listener #51 and #52 are attached to light switches, and
     those aren't usually written to in every frame. In the Seneca they
     are, though ...   :-)