[HOpenGL] HOpenGL and --enable-threaded-rts

[Wolfgang Thaller]

Simon Peyton-Jones wrote:
> The idea would be that we'd keep the invariant that only one OS
> thread can be executing Haskell at any moment.  So no mutex locks on
> allocation or thunk entry.

Ah that sounds good. I think I can live with some OS-thread-switching. I 
think this is the way to go. Is anyone available to implement this? (How 
long will I have to keep using my own ugly hack?)

> Suppose we call one of a Haskell-thread-with-a-dedicated-OS-thread
> a "Haskell super-thread"

I'd suggest "heavy threads" vs. "light threads" :-).

Claus Reinke wrote:
>  I still like Sven's idea - noone has asked
> for a new OS thread for the callbacks, so there shouldn't be one, so
> there shouldn't be a problem with the admittedly not nice use of
> OS-thread-local storage.

The problem with that is that it will fail miserably (read: crash) if 
another haskell thread does something that _requires_ an OS thread 
switch (like call a foreign import threadsafe function).

Sven Panne wrote:
> Furthermore,
> it would be extremely system-dependent and would cost a *vast* amount of
> performance: Switching OpenGL contexts can require a round-trip to a
> remote server, can trigger swapping a few MB of textures into your
> favourite graphics card, etc.

I don't think so. Context-switching is a client-side affair. After all, 
a single-threaded two-window OpenGL application has to switch between 
its two contexts all the time.

Cheers,
Wolfgang