说明：  线程池原理及创建(C++实现) 本文给出了一个通用的线程池框架，该框架将与线程执行相关的任务进行了高层次的抽象，使之 与具体的执行任务无关。另外该线程池具有动态伸缩性，它能根据执行任务的轻重自动调整线程 池中线程的数量。
(Principle and create a thread pool (C++ implementation) In this paper, a common thread pool framework, the framework will perform the related tasks and threads a high level of abstraction, so that has nothing to do with the specific tasks. In addition, the thread pool with dynamic scalability, the number of thread pool threads can automatically adjusted according to the severity of the tasks.)