KML asynchronous load in osgEarth

gistfile1.txt

#include <osgViewer/Viewer>
#include <osgEarthUtil/EarthManipulator>
#include <osgEarthUtil/ExampleResources>
#include <osgEarth/MapNode>
#include <osgEarth/ModelLayer>
#include <osgEarthDrivers/kml/KML>
#include <osg/ProxyNode>

using namespace osgEarth;
using namespace osgEarth::Util;
using namespace osgEarth::Drivers;

int main(int argc, char** argv)
{
    osg::ArgumentParser arguments(&argc,argv);

    osgViewer::Viewer viewer(arguments);
    viewer.setCameraManipulator(new EarthManipulator());

    osg::Node* node = MapNodeHelper().load(arguments, &viewer);
    viewer.setSceneData( node );
    MapNode* mapNode = MapNode::get(node);

    std::string kmlFile("../data/KML_Samples.kml");

    // Set up your KML defaults... optional but a good idea
    KMLOptions kml_options;
    kml_options.declutter() = true;

    // Icon for point placemarks:
    IconSymbol* defaultIcon = new IconSymbol();
    defaultIcon->url()->setLiteral("../data/placemark32.png");
    kml_options.defaultIconSymbol() = defaultIcon;

    // Text appearance:
    TextSymbol* defaultText = new TextSymbol();
    defaultText->halo() = Stroke(0.3, 0.3, 0.3, 1.0);
    kml_options.defaultTextSymbol() = defaultText;

    // Pass the MapNode and your KML Options to the loader in an Options structure:
    osgDB::Options* dbOptions = new osgDB::Options();
    dbOptions->setPluginData("osgEarth::MapNode", mapNode);
    dbOptions->setPluginData("osgEarth::KMLOptions", (void*)&kml_options);

    // Set up a proxy node that will load asynchronously in a pager thread:
    osg::ProxyNode* proxy = new osg::ProxyNode();
    proxy->setFileName(0, kmlFile);
    proxy->setLoadingExternalReferenceMode(proxy->DEFER_LOADING_TO_DATABASE_PAGER);
    proxy->setDatabaseOptions(dbOptions);

    // Install in the scene graph!
    mapNode->addChild(proxy);

    return viewer.run();
}