__attribute__机制介绍

http://blog.sina.com.cn/s/blog_79382a9301013mnm.html

http://blog.csdn.net/sunboy_2050/article/details/6566739

__block 

http://code.google.com/p/nevel-mercury/wiki/GetFamiliarWithBlock

http://blog.csdn.net/kmyhy/article/details/6447287