/**
* Create and get a lock
* @param string $resource - The identifier for the lock. Should use frankenstyle prefix.
* @param int $timeout - The number of seconds to wait for a lock before giving up.
* @param int $maxlifetime - Unused by this lock type.
* @return boolean - true if a lock was obtained.
*/
public function get_lock($resource, $timeout, $maxlifetime = 86400)
{
$token = $this->generate_unique_token();
$now = time();
$giveuptime = $now + $timeout;
$expires = $now + $maxlifetime;
if (!$this->db->record_exists('lock_db', array('resourcekey' => $resource))) {
$record = new \stdClass();
$record->resourcekey = $resource;
$result = $this->db->insert_record('lock_db', $record);
}
$params = array('expires' => $expires, 'token' => $token, 'resourcekey' => $resource, 'now' => $now);
$sql = 'UPDATE {lock_db}
SET
expires = :expires,
owner = :token
WHERE
resourcekey = :resourcekey AND
(owner IS NULL OR expires < :now)';
do {
$now = time();
$params['now'] = $now;
$this->db->execute($sql, $params);
$countparams = array('owner' => $token, 'resourcekey' => $resource);
$result = $this->db->count_records('lock_db', $countparams);
$locked = $result === 1;
if (!$locked) {
usleep(rand(10000, 250000));
// Sleep between 10 and 250 milliseconds.
}
// Try until the giveup time.
} while (!$locked && $now < $giveuptime);
if ($locked) {
$this->openlocks[$token] = 1;
return new lock($token, $this);
}
return false;
}
/**
* @param moodle_database $db the database connection to use to access the cache.
* @return int the number of entries in the cache.
*/
public static function entries_count($db)
{
return $db->count_records('qtype_stack_cas_cache');
}
