GCD

• 获得主队列

 dispatch_queue_t mainQueue = dispatch_get_main_queue();

• 获得全局队列

dispatch_queue_t gloableQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

• 串行队列

 dispatch_queue_t queue = dispatch_queue_create("myqueue", DISPATCH_QUEUE_SERIAL);

• 异步队列

    dispatch_async(queue, ^{
        
    });

• 同步队列

dispatch_sync(queue, ^{
       
   });

• 阻隔队列 (像栅栏一样 ) 例如 A -->栅栏 --> B 有序

dispatch_barrier_async(queue, ^{
        NSLog(@"----barrier-----%@", [NSThread currentThread]);
    });

• eg :异步线程加载图片

-(void)asyncSetImage{
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        
        NSURL *url = [NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/8/1/9981681/200910/11/1255259355826.jpg"];
        
        // 加载图片
        NSData *data = [NSData dataWithContentsOfURL:url];
        
        //生成图片
        UIImage *image = [UIImage imageWithData:data];
        
        dispatch_async(dispatch_get_main_queue(), ^{
           
            self.imageView.image = image;
        });
        
    });
}