     }
     
     public func enumerateKeysWith(predicate: NSPredicate?, backward: Bool, startingAtKey key: String?, andPrefix prefix: String?, callback: LevelDBKeyCallback) {
-        //serialQueue.smartSync {
         guard let db = db else {
             NSLog("Database reference is not existent (it has probably been closed)")
             return

            free(rawData)
            result = true
        }
        //}
        return result
    }
    
    public func removeValueForKey(_ key: String) {
        //serialQueue.smartSync {
        guard let db = db else {
            NSLog("Database reference is not existent (it has probably been closed)")
            return

            }
            backward ? levelDBIteratorMoveBackward(iterator) : levelDBIteratorMoveForward(iterator)
        }
        levelDBIteratorDelete(iterator)
    }
    
    // MARK: - Helper methods
