Hi Jon, Thanks for the reply. From what I read about the GIL, I thought it was something inherent in Python and not controllable. Are you sure that releasing the GIL during the Mapnik render is not just declaring to the Python runtime that a switch of thread execution can take place here? i.e. a thread safe area.
Here's a Wiki entry on GIL: http://en.wikipedia.org/wiki/Global_Interpreter_Lock The bit I noted was " Applications written in languages with a GIL have to use separate processes (i.e. interpreters) to achieve full concurrency, as each interpreter has its own GIL.". Doesn't this suggest that to use multiple cores/processors for tiling, separate processes are the way to go rather than multiple threads? Threading looks pretty simple in Python so I'll look at doing some performance tests myself. Regards, Warren -----Original Message----- From: Jon Burgess [mailto:[email protected]] Sent: 06 September 2009 10:46 To: Warren Vick Cc: [email protected] Subject: Re: [Mapnik-users] Multi Threading 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. Jon _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
