if (len % 8 == 0) { // Allocate data in 8-piece slabs
        void *new_data;
        int *new_sizes;
        printf("arg_pack has no capacity\n");
        if ((new_data = realloc(args->data, len + 8*sizeof(void*))) == NULL)
            return 0;
        else if ((new_sizes = realloc(args->sizes, len + 8*sizeof(int))) == NULL)
            return 0;
        printf("After realloc\n");