     *
     *  @return
     */
-    class func once(predicate: UnsafePointer<dispatch_once_t>, closure: GCDClosure) {
+    class func once(predicate: UnsafeMutablePointer<dispatch_once_t>, closure: GCDClosure) {
         dispatch_once(predicate, closure)
     }
 }
    *  @param label (can be nil)
    */
    init(serial label: String?) {
        if label {
            dispatchQueue = dispatch_queue_create(label!, DISPATCH_QUEUE_SERIAL)
        }
        else {

    *  @param label (can be nil)
    */
    init(concurrent label: String?) {
        if label != nil {
            dispatchQueue = dispatch_queue_create(label!, DISPATCH_QUEUE_CONCURRENT)
        }
        else {
