[Bf-committers] Pretty clueless Linux threads crashing...

Chris Want cwant at ualberta.ca
Thu Feb 23 19:58:52 CET 2006

Hi Ton,

I haven't been able to replicate your crashes here -- do
you have a blend file that is known to be volatile?

One thing I have noticed is that the render window only
seems to update the scanlines of one tile now (it used
to update two tiles) -- is that a bug, or a feature?


Ton Roosendaal wrote:
> Hi all,
> I need help locating what goes wrong in using thread render on Linux.  
> I'm using SDL for threads, and it appears that in Linux threads refuse  
> to close (well, gdb reports lotsof zombies to end), and after a while  
> (unpredictable, but on some scenes every render) it ends with this:
> #0  0xb781bcda in sem_post at GLIBC_2.0 () from  
> /lib/tls/i686/cmov/libpthread.so.0
> (gdb) bt
> #0  0xb781bcda in sem_post at GLIBC_2.0 () from  
> /lib/tls/i686/cmov/libpthread.so.0
> #1  0xb7ba2748 in SDL_SemPost () from /usr/lib/libSDL-1.2.so.0
> #2  0xb7ba1efb in SDL_RunThread () from /usr/lib/libSDL-1.2.so.0
> #3  0xb7ba21d1 in SDL_KillThread () from /usr/lib/libSDL-1.2.so.0
> #4  0xb7817361 in start_thread () from  /lib/tls/i686/cmov/libpthread.so.0
> #5  0xb7912bde in clone () from /lib/tls/i686/cmov/libc.so.6
> Note; I am using SDL_KillThread() now instead of the official  
> SDL_WaitThread(), because that seems to be more *stable*... using  
> SDL_WaitThread() gives same crashes.
> I also have no idea what this bt means... why would the KillThread call  
> a RunThread and then hang in sem_post()???
> Some clues;
> - it seems to happen more often when OpenGL is busy too. Like with huge  
> windows it crashes more often. I do know that within a thread you  
> should not use X11 or opengl, using windows/events/opengl calls in  
> threads won't work on OSX either. Nevertheless, we did try Brecht's  
> hint, to add XInitThreads() in GHOST_SystemX11.cpp, before line 107.  
> Didn't really give improvements.
> - when rendering without threads button pressed, rendering goes OK. The  
> render code then still uses a single SDL thread for the tile render  
> though.
> - On different Linux installs we get different reports. Some report  
> crashes all the time, some claim its running fine.
> - In OSX threads never crash this way, nor do we get zombie threads.  
> OSX does have a quite rare opengl crash though, which also only seems  
> to happen while using huge windows.
> - I've very carefully checked all code to see if there's any  
> opengl/event call during a thread, but couldn't find one. Still might  
> be there though... maybe I'm just missing some.
> - I'm not using semaphores code, but do have Mutex to protect the  
> MEM_malloc calls.
> The way I am using SDL threads for rendering:
> - the main loop (not a thread) is in render module, pipeline.c,  
> threaded_tile_processor()
> - this loop goes to sleep when all 'thread slots' are filled.
> - 20 times per second it wakes up, and either draws a scanline part  
> update, or the entire tile
> - if a thread is finished, it sets a flag in the RenderPart struct to  
> indicate that, then the mainloop makes sure a SDL_WaitThread is called  
> (SDL_KillThread now)
> I moved all threading code to blenlib/intern/threads.c. In the c file  
> you can see docs for usage of the functions. Here also the mutexes are  
> set and used for mallocs.
> Hopefully someone reads this with SDL coding experience! :)
> -Ton-
> ------------------------------------------------------------------------ --
> Ton Roosendaal  Blender Foundation ton at blender.org  http://www.blender.org
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