腾讯总考epoll, 很烦

腾讯面试每次都考epoll, 说真的，很烦。 

很多面试官自己的知识不进化，天天只记得个epoll, 还说什么呢？

[email protected]:~$ man epoll
EPOLL(7)                                             Linux Programmer's Manual                                            EPOLL(7)

NAME
       epoll - I/O event notification facility

SYNOPSIS
       #include <sys/epoll.h>

DESCRIPTION
       The  epoll API performs a similar task to poll(2): monitoring multiple file descriptors to see if I/O is possible on any of
       them.  The epoll API can be used either as an edge-triggered or a level-triggered interface and scales well to  large  num[m
       bers of watched file descriptors.  The following system calls are provided to create and manage an epoll instance:

       *  epoll_create(2)  creates  an  epoll instance and returns a file descriptor referring to that instance.  (The more recent
          epoll_create1(2) extends the functionality of epoll_create(2).)

       *  Interest in particular file descriptors is then registered via epoll_ctl(2).  The set of file descriptors currently reg[m
          istered on an epoll instance is sometimes called an epoll set.

       *  epoll_wait(2) waits for I/O events, blocking the calling thread if no events are currently available.

   Level-triggered and edge-triggered
       The epoll event distribution interface is able to behave both as edge-triggered (ET) and as level-triggered (LT).  The dif[m
       ference between the two mechanisms can be described as follows.  Suppose that this scenario happens:

       1. The file descriptor that represents the read side of a pipe (rfd) is registered on the epoll instance.

       2. A pipe writer writes 2 kB of data on the write side of the pipe.

       3. A call to epoll_wait(2) is done that will return rfd as a ready file descriptor.

       4. The pipe reader reads 1 kB of data from rfd.

       5. A call to epoll_wait(2) is done.

其实，这就是八股文题目，没啥意思。