/**
* Ensures there is only one instances of LEM. Note, if switch between surveys, have to clear this cache
* @return LimeExpressionManager
*/
public static function &singleton()
{
$now = microtime(true);
if (isset($_SESSION['LEMdirtyFlag'])) {
$c = __CLASS__;
self::$instance = new $c();
unset($_SESSION['LEMdirtyFlag']);
} else {
if (!isset(self::$instance)) {
if (isset($_SESSION['LEMsingleton'])) {
self::$instance = unserialize($_SESSION['LEMsingleton']);
} else {
$c = __CLASS__;
self::$instance = new $c();
}
} else {
// does exist, and OK to cache
return self::$instance;
}
}
// only record duration if have to create (or unserialize) an instance
self::$instance->runtimeTimings[] = array(__METHOD__, microtime(true) - $now);
return self::$instance;
}
