多线程监控

  dispatch_queue_t dispatchQueue = dispatch_queue_create("ted.queue.next",DISPATCH_QUEUE_CONCURRENT);
                dispatch_group_t dispatchGroup = dispatch_group_create();
                dispatch_group_async(dispatchGroup, dispatchQueue, ^(){
                    for (NSInteger i = 0; i < self.messageArray.count; i ++) {
                        totalHeight = totalHeight + [self getCellHeight:self.messageArray[i] WithIsLastRow:self.messageArray.count - 1 == i WithIndexRow:i];
                    }
                });
                dispatch_group_notify(dispatchGroup,dispatch_get_main_queue(), ^(){
                    if (totalHeight > self.table.height) {
                        CGPoint offset = CGPointMake(0,ceil(totalHeight) - ceil(self.table.height) );
                        [self.table setContentOffset:offset animated:NO];
                    }
                    [self.table reloadData];

                });