你知道睡眠（）/ usleep() / nanosleep()不好延迟的问题。

代码说明：

As you have learnt that sleep( )/usleep()/nanosleep() are not good to delay a process. Timers can provide more accurate time control in applications. In this lab, you will explore POSIX timers and signal programming, experience the timer drift. The primary focus of this lab will be "time". The experiment will show you several methods to measure time in your applications.