/**
* Get the name of the lock to use specific to the database name of the current application, as a SQL-escaped string.
*/
protected static function lockNamePostfix()
{
if (!self::$lockNamePostfix) {
self::$lockNamePostfix = Convert::raw2sql('_' . DB::query('select database()')->value());
}
return self::$lockNamePostfix;
}
/**
* Returns a single queue object according to a particular priority and freshness measure.
* This method removes any duplicates and makes the object as "regenerating", so other calls to this method
* don't grab the same object.
* If we are using MySQLDatabase with InnoDB, we do row-level locking when updating the dataobject to allow for
* distributed cache rebuilds
* @static
* @param $freshness
* @param $sortOrder
*/
protected static function get_queue_object($freshness, $interval = null, $sortOrder = array('Priority' => 'DESC', 'ID' => 'ASC'))
{
$className = __CLASS__;
$queueObject = null;
$filterQuery = array("Freshness" => $freshness);
if ($interval) {
$filterQuery["LastEdited:LessThan"] = $interval;
}
$query = self::get();
if ($query->Count() > 0) {
$offset = 0;
$filteredQuery = $query->filter($filterQuery)->sort($sortOrder);
if ($filteredQuery->Count() > 0) {
if (DB::getConn() instanceof MySQLDatabase) {
//locking currently only works on MySQL
do {
$queueObject = $filteredQuery->limit(1, $offset)->first();
//get first item
if ($queueObject) {
$lockName = md5($queueObject->URLSegment . $className);
}
//try to locking the item's URL, keep trying new URLs until we find one that is free to lock
$offset++;
} while ($queueObject && !LockMySQL::isFreeToLock($lockName));
if ($queueObject) {
$lockSuccess = LockMySQL::getLock($lockName);
//acquire a lock with the URL of the queue item we have just fetched
if ($lockSuccess) {
self::remove_duplicates($queueObject->ID);
//remove any duplicates
self::mark_as_regenerating($queueObject);
//mark as regenerating so nothing else grabs it
LockMySQL::releaseLock($lockName);
//return the object and release the lock
}
}
} else {
$queueObject = $filteredQuery->first();
self::remove_duplicates($queueObject->ID);
self::mark_as_regenerating($queueObject);
}
}
}
return $queueObject;
//return the object or null
}
