Re-organized the access of the mutex in Terrain to avoid deadlocks, and temporarily switched off the update of the neightbouring tile boundaries within the GeometryTechnique::generateGeometry method, again to avoid deadlocks.

src/osgTerrain/GeometryTechnique.cpp

@@ -903,7 +903,7 @@ void GeometryTechnique::generateGeometry(BufferData& buffer, Locator* masterLoca
 
         _neighbours.clear();
 
-        bool updateNeighboursImmediately = true;
+        bool updateNeighboursImmediately = false;
 
         if (left_tile.valid())   addNeighbour(left_tile.get());
         if (right_tile.valid())  addNeighbour(right_tile.get());

src/osgTerrain/Terrain.cpp

@@ -83,16 +83,22 @@ void Terrain::traverse(osg::NodeVisitor& nv)
         // need to check if any TerrainTechniques need to have their update called on them.
         osgUtil::UpdateVisitor* uv = dynamic_cast<osgUtil::UpdateVisitor*>(&nv);
         if (uv)
+        {
+            typedef std::list< osg::ref_ptr<TerrainTile> >  TerrainTileList;
+            TerrainTileList tiles;
             {
                 OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_mutex);
-            for(TerrainTileSet::iterator itr = _updateTerrainTileSet.begin();
+                std::copy(_updateTerrainTileSet.begin(), _updateTerrainTileSet.end(), std::back_inserter(tiles));
-                itr != _updateTerrainTileSet.end();
+                _updateTerrainTileSet.clear();
+            }
+
+            for(TerrainTileList::iterator itr = tiles.begin();
+                itr != tiles.end();
                 ++itr)
             {
                 TerrainTile* tile = *itr;
                 tile->traverse(nv);
             }
-            _updateTerrainTileSet.clear();
         }
     }