/**
* Creates a new singleton application server instance.
*
* @param \AppserverIo\Psr\Naming\NamingDirectoryInterface $configurationFilename The default naming directory
* @param \AppserverIo\Storage\GenericStackable $runlevels The storage for the services
*
* @return \AppserverIo\Appserver\Core\Interfaces\ApplicationServerInterface The singleton application instance
*/
public static function singleton(NamingDirectoryInterface $namingDirectory, GenericStackable $runlevels)
{
// query whether we already have an instance or not
if (ApplicationServer::$instance == null) {
// initialize and start the application server
ApplicationServer::$instance = new ApplicationServer($namingDirectory, $runlevels);
ApplicationServer::$instance->start();
}
// return the instance
return ApplicationServer::$instance;
}
