private void updateQuadLODs() {

        if (indexer == null || !indexer.isDone()) {
            return;
        }

        try {

            final HashMap<String, UpdatedTerrainPatch> updated = indexer.get();
            if (updated != null) {
                // do the actual geometry update here
                for (final UpdatedTerrainPatch utp : updated.values()) {
                    utp.updateAll();
                }
            }

        } catch (final InterruptedException | ExecutionException ex) {
            Logger.getLogger(TerrainLodControl.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            indexer = null;
        }
    }
Back on the ogl thread: update the terrain patch geometries
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainLodControl.java