首先，引用官方文档中的解释:

The reactor is Twisted's main event loop. There is exactly one reactor in any running Twisted application. Once started it loops over and over again,responding to network events,and making scheduled calls to code. 也就是说reactor是twisted中主要的事件循环。每个twisted应用都必须要使用一个reactor，当它启动之后就会不停地进行循环操作，对网络事件进行响应，并对程序进行调度。 未完待续...