Hi Ola, I've been doing a code review of Terrain and TerrainTile looking at how deletion of TerrainTile will affect the internal TerrainTile pointers held in Terrain that track all the tiles. There internal TerrainTile pointers in Terrain are protected by a reentrant mutex but I believe a problem can occur when the TerrainTile destructor calls Terrain::unregisterTerrainTile(TerrainTile*) when at the same time the Terrain::traverse(NodeVisitor&) method is taking a copy of the _updateTerrainTileSet, when this occurs the update traversal would increment the ref count on an TerrainTile being destructed by the DatabasePager thread that is cleaning up expired tiles.
This issue boils down to attempt to make a thread safe list TerrainTile observers in Terrain that doesn't quite achieve what it intends. I haven't thought deeply enough about the issue yet to know what the best solution will be. My head isn't quite into zone that will allow me to solve this one so I'll have to come back to it at a later date. A short term solution would be set the pager so that it doesn't delete objects in a background pager thread via DatabasePager::setDeleteRemovedSubgraphsInDatabaseThread(false), this won't fix the thread safety issue but will at least prevent the particular instance where the update traversal is occurring at the same time as the deletion of TerrainTile. Robert. _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
