static public function start( $flags = 0, $options = array() )
    {
        if ( !extension_loaded( 'xhprof' ) )
        {
            eZPerfLoggerDebug::writeWarning( 'Extension xhprof not loaded, can not start profiling', __METHOD__ );
            return false;
        }
        xhprof_enable( $flags + XHPROF_FLAGS_CPU + XHPROF_FLAGS_MEMORY, $options );
        self::$profilingRunning = true;
        return true;
    }