On Sun, 2009-09-06 at 10:46 +0100, Jon Burgess wrote:
>
> On Sun, 2009-09-06 at 09:28 +0100, Warren Vick wrote:
> > I've just discovered that Python is a language which does not let
> > multiple threads execute at the same time, because the run parallel
> > runtime support is based on a central lock (the "Global Interpreter
> > Lock"). So, I guess the only way to utilise multiple
> processors/cores
> > is to run separate processes? Or, do all Python programs running on
> a
> > system share the same runtime?
>
> Mapnik can render lots of tiles in parallel via the python bindings.
> The
> GIL is released during the main rendering call so that multiple
> threads
> can run in parallel. I use the feature in the python mod_tile
> renderd.py.
>
> The generate_tiles.py has not been updated because it was originally
> intended as a simple example program, not a serious tool for rendering
> millions of tiles. I'll take a look at adding in some multithreading
> into generate_tiles.py.
I have checked in a version of generate_tiles.py which uses multiple
rendering threads. On a 2 core machine this reduces the rendering time
for the "world 0 - 4" tiles from 35 to 23 seconds.
The new code also makes use of some of the more recent Mapnik features
like the buffer_size and png256 output format.
Jon
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