Background thread

    dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

            // Add code here to do background processing

            dispatch_async( dispatch_get_main_queue(), ^{

                // Add code here to update the UI/send notifications based on the

                // results of the background processing

            });

        });

(OR)

    dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){

            // Add code here to do background processing

            dispatch_async( dispatch_get_main_queue(), ^(void){

                // Add code here to update the UI/send notifications based on the

                // results of the background processing

            });

        });