NSThread

  [NSThread sleepForTimeInterval:2];//让线程睡两秒
    [NSThread sleepUntilDate:[NSDate date]];//让线程睡到指定的日期点
    //用NSThread新建子线程
    [NSThread detachNewThreadSelector:@selector(go) toTarget:self withObject:nil];


-(void)go
{
    NSLog(@"%@",[NSThread currentThread]);
    NSData *data = [[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:@"http://d.hiphotos.baidu.com/image/pic/item/9922720e0cf3d7ca60432a7df41fbe096b63a907.jpg"]];
    dispatch_async(dispatch_get_main_queue(), ^{
        _imageback2.image = [UIImage imageWithData:data];
    });
}