protected function setKeyTTL($key, $ttl)
{
if ($this->acquire_key($this->ttl_table_name, $AutoUnlocker)) {
$ttl_table = $this->memcache->get($this->ttl_table_name);
$ttl_table[$key] = $ttl;
$this->memcache->set($this->ttl_table_name, $ttl_table);
$this->unlock_key($AutoUnlocker);
}
}