单例模式+加锁+多线程

http://www.cnblogs.com/cxjchen/p/3148582.html

http://blog.csdn.net/hackbuteer1/article/details/7460019 C++加锁封装

http://blog.csdn.net/joanlynnlove/article/details/7462254 pthread加锁封装   打印日志

http://www.xuebuyuan.com/687289.html  引用的作用，否则出错