[Gridflow-dev] [PD] OpenMP and Pd

Claude Heiland-Allen claudiusmaximus at goto10.org
Mon Dec 6 05:34:05 EST 2010

Hi Pedro,

Somehow I thought this was a new message, but the date tells me it's 
from quite some time ago.  Replying anyway as it may be interesting to 
you and all:

On Thu, May 20, 2010 at 4:46 PM, Pedro Lopes<pedro.lopes at ist.utl.pt> 
wrote something roughly along the lines of:
 > I was trying to include pragma comments of OpenMp in a PD external,
 > but it does not seem to work for some reason.
 > undefined symbol: GOMP_parallel_start

OpenMP has a run time system that is linked into the executable when you 
compile with -fopenmp - if you compile a shared object (like a Pd 
external) with -fopenmp it hopes that the executable that loads it will 
have the OpenMP run time system inside it.  So the fix is simple: just 
compile Pd itself with -fopenmp, then compile your external with 
-fopenmp too, and it should Just Work (TM).  Attached patch against 
pd-0.42-5 allowed me to load a slightly modified version of gridflow and 
see Pd using more than one core:


(After applying the patch, run "autoreconf" to regenerate "./configure")

NB: while it does use more than one core, I just compared with the 
single core version of gridflow without openmp and it uses only 25% of 
my cpu (on one core) while the openmp version uses 145% of my cpu 
(spread over two cores).  So, it's no magic bullet...

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