In preparation for the next major release of OpenStreetBrowser, which will allow users to create specialized maps themselves, I made a patch to mod_tile. Mod_tile is an extension for Apache which efficiently delivers map tiles and on demand (re-)renders them (or lets say it contacts renderd or tirex to request a re-renderding). Currently only the time stamp of the planet-file and the tile are compared, but with this patch it also compares the time stamp of the style definition.
Therefore the style can be updated and the tiles will be re-rendered (if there's still CPU power available). It still needs a restart of renderd to reload the style-definition.
Download the patch here.