解决读者－写者的想法：

就是所谓的”忙等待“。一个进程（线程）要使用某个资源，先看能否满足”一定要求“，能，就使用，

不能就等待直到这个要求满足为止。

-Solve the readers- the idea of writing: the so-called " busy waiting."　A process (thread) to use a resource, look at the can meet the " demands" , to the use, can not wait to meet this requirement until the date.