Hamish wrote:
> in making some of the python modules multithreaded, it would
> be useful to have a version of grass.mapcalc() which didn't
> wait until it was done, and returned the Popen object instead.
>
> e.g. to process three r,g,b bands in parallel.
>
> I just added an experimental grass.mapcalc_start() fn to
> trunk/lib/python/raster.py,
an example for running 3 r.mapcalcs in parallel:
before:
grass.mapcalc('%s.red = r#%s' % (out, in_R))
grass.mapcalc('%s.grn = g#%s' % (out, in_G))
grass.mapcalc('%s.blu = b#%s' % (out, in_B))
after:
pr = grass.mapcalc_start('%s.red = r#%s' % (out, in_R))
pg = grass.mapcalc_start('%s.grn = g#%s' % (out, in_G))
pb = grass.mapcalc_start('%s.blu = b#%s' % (out, in_B))
pr.wait()
pg.wait()
pb.wait()
since the parent process retains control of the pipes by default,
AFAIK p.communicate() is not needed here, errors and messages
just get propagated to the terminal as they occur.
Hamish
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