搞懂这篇文章，关于IO复用的问题就信手拈来了

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以一个生活中的例子来解释.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"假设你在大学中读书,要等待一个朋友来访,而这个朋友只知道你在A号楼,但是不知道你具体住在哪里,于是你们约好了在A号楼门口见面.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果你使用的阻塞IO模型来处理这个问题,那么你就只能一直守候在A号楼门口等待朋友的到来,在这段时间里你不能做别的事情,不难知道,这种方式的效率是低下的.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"进一步解释select和epoll模型的差异.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"select版大妈做的是如下的事情:比如同学甲的朋友来了,select版大妈比较笨,她带着朋友挨个房间进行查询谁是同学甲,你等的朋友来了,于是在实际的代码中,select版大妈做的是以下的事情:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"int n = select(&readset,NULL,NULL,100); \nfor (int i = 0; n > 0; ++i) {\n if (FD_ISSET(fdarray[i], &readset)) {\n do_something(fdarray[i]); --n; \n } \n}\n123456","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"epoll版大妈就比较先进了,她记下了同学甲的信息,比如说他的房间号,那么等同学甲的朋友到来时,只需要告诉该朋友同学甲在哪个房间即可,不用自己亲自带着人满大楼的找人了.于是epoll版大妈做的事情可以用如下的代码表示:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"n = epoll_wait(epfd,events,20,500);","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"for(i=0;i