Call method after every 1 sec. in Background thread

First time call through:

//call from viewdidload

dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

    dispatch_async(q_background, ^{

        [self checkFileOpenOrNot:nil];

   });

-(void) checkFileOpenOrNot:(id)sender{

//do your code 

dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

            double delayInSeconds = 1.0;

            dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);

            dispatch_after(popTime, q_background, ^(void){

                [self checkFileOpenOrNot:nil];

            });

}