epoll is a Linux kernel system call for a scalable I/O event notification mechanism
wiki 解释，是一种 linux 可扩展 io 事件通知机制的系统调用
系统调用，In computing, a system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on.
在计算机领域，系统调用是请求执行操作系统内核的的一种编程方式
内核，The kernel is a computer program that is the core of a computer's operating system, with complete control over everything in the system.
内核是对操作系统核心进行的处理的电脑程序。
epoll -> kernel -> os ， 想要了解 epoll ，就要了解 linux 内核， linux 内核代表了对操作系统进行调用的程序。 linux 操作系统 是软件对计算机硬件的抽象。
