关于锁

static Object lock = [Object alloc] init];
int count = _dataArray.count;
for(int i = 0; i < count ; i ++ )
{
UploadModel *model = _dataArray;
UploadManager *manager = [[UploadManager alloc] init];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[manager uploadImagesWithSelecteArray: model success:^{

                // 上传成功回调   删除_dataArray中的数据
               //为什么要加个锁,因为每个任务结束的时间是不一样的,block也会开子线程,你获得了某个index后,cpu青睐了其他线程,然后执行了[_dataArray removeObject: model],你之前获得的index就是错误的index,所以你要加个锁,锁住这块代码,等这块代码执行完,才会放开这个锁.这样你上传是异步的,成功之后删除数组,更新Ui都是同步的,这样不会出现异步造成的错误
          @synchronized (lock) {   
                NSInteger index = [_dataArray indexOfObject: model];
                NSIndexPath *indexPath = [NSIndexPath indexPathForRow:index inSection:0];
                [_dataArray removeObject: model];
                //  删除对应的Cell
                dispatch_async(dispatch_get_main_queue(), ^{
                  [_tableView deleteRowsAtIndexPaths:[NSArray arrayWithObjects:indexPath, nil] withRowAnimation:UITableViewRowAnimationTop];
               });
             }
            } failure:^{
                NSLog(@"上传失败提示");
            }];
           
        });

}