GCD doesn't work in custom keyboard

Question

please can anyone help me? I have next problem. I created custom keyboard in xcode and want to use the GCD to load gifs async in array. But when i do this my app crash. My code

@implementation KeyboardViewController 

in viewDidLoad ()

dispatch_queue_t myQueue = dispatch_queue_create("identifier", NULL);

    dispatch_async(myQueue, ^{

        @synchronized (self.gifsArray){
            @autoreleasepool {
                for (int i = 0; i < NUMBER_OF_GIFS; i++) {
                    FLAnimatedImage *gifImage = [[FLAnimatedImage alloc] initWithAnimatedGIFData:[NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:@"%i", i] ofType:@"gif"]]];
                    [self.gifsArray addObject:gifImage];
            }

        }
        }
    });