Re: [PyOpenGL-Users] glutSetWindow in a thread segfaults

[Mike C. F. <mcf...@vr...>]

Ulas Türkmen wrote:
...
> The Image object is from PIL. As you can see, thread locks are
> necessary to stop the display functions from changing the displays;
> otherwise, an OpenGL error is thrown.
>
> When this routine is called from the display class of which it is a
> member, there are no errors; the image is saved in the given path.
> When it is called from outside the thread, however, glutSetWindow
> causes a segmentation fault. This happens not each and every time but
> most of the time, which puzzled me even more. Before we put in locks
> for the drawing functions, segfaults and OpenGL errors would each
> happen.
>   
I would have been surprised had it worked, actually.  Most GUI libraries 
are inherently non-thread-safe and will mess up rather badly when you 
try to call functions from another thread.  Normally you get around this 
by having a queue of tasks to accomplish in the GUI thread and adding 
your operation to that queue.  The GUI thread checks the queue 
(non-blocking) and executes the operations when it is in a stable state, 
returning the result on another queue that you (the client code) wait on 
(blocking).

Not to say you *couldn't* make it work with enough locks and the like, 
but I'd be tempted to go with an "all GUI code in one thread" approach 
for stability.

HTH,
Mike

-- 
________________________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://www.vrplumber.com
  http://blog.vrplumber.com