Re: [Flightgear-devel] multi-threading

[VS R. <aki...@ya...>]

Curt,

> I don't know specifically what could be wrong.  But, you need to
> ensure that ***every*** opengl call is made from only one thread, and
> no opengl calls are made from any other thread.  This includes
> configuring lighting, setting up the view frustum, fog, texture
> loading, model loading, etc.  Otherwise, the opengl calls can get
> mixed arbitrarily from the different threads, and since OpenGL is a
> "state machine" this can cause terrible problems and usually ends up
> in a crash.  Imagine intermixing texture load calls with the render
> thread.  You end up with illegal calls being made inside a glBegin() /
> glEnd() and this is just the start of the bad stuff that can happen.
>
> You could protect the opengl sections with semaphores somehow, but
> then you will probably lose any benefits of threading the render loop.
>

I understand. I have played around with Performer on our OnyxRE2 and that is
why
I tried the renedering thread. We are now going to attempt something like
this to overcome the problem of *invisible textures* :
- initialisation + rendering (FgRenderFrame() function) in the main thread
- tile-paging in another thread
- all the rest (network, keyboard etc.) in another ( I dont know whether
this is non-trivial).

I *want* to try it out in order to make the best use of our dual processor
machines. Under Win2k
I find that while running FlighGear alone one processor is about 60-70%
loaded and other about 20-30% loaded. I wish to improve that.

> This all is very much non-trivial to do, and I'm not sure how much of
> a win it would be overall in terms of performance.

Can someone tell me why it wont improve overall performance on dual
processor machines even if I get it right?.

>but my gut feeling would be that threading should
> probably be addressed inside plib.  However, this is very much
> non-trivial, and Steve speaks of the immense contortions that the
> Performer development team had to go through to get this all right for
> their scene graph.

Their model of application+cull+draw works very well on the OnyxRE2. Let me
see if a similar model works with FlightGear!!!. If someday Steve gets all
that into PLib then maybe.... I'll try till then.

Regards
Ranga



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