epoll.md

epoll

参考: IO 多路复用是什么意思？ - 罗志宇的回答 - 知乎 https://www.zhihu.com/question/32163005/answer/55772739

原补丁: http://www.xmailserver.org/linux-patches/nio-improve.html

man page: http://www.xmailserver.org/linux-patches/epoll_create.txt

socket 源码: https://www.cnblogs.com/sddai/p/5790414.html

IO多路复用

单个线程通过记录跟踪每一个Sock(I/O流)的状态.

其中包含了 复用/解复用 的概念.

https://blog.csdn.net/qq_31833457/article/details/78495354

很多链接进来，epoll 会把他们都监视起来，然后像拨开关一样，谁有数据就拨向谁，然后调用相应的代码处理。

https://suchprogramming.com/epoll-in-3-easy-steps/

水平触发: 若一次读取数据没有读完,下次仍可读: 边缘触发: 若一次读取数据没有读完,下次不可读: 只在状态改变时传递数据

select 和 poll 只支持水平触发.

1. Set up your accept socket ...
2. Add to epoll.
3. enter wait loop:
   1. Check whether event is on accept socket, or normal socket
   2. If accept socket, accept connection, add to epoll, go back to 3
   3. If event on normal socket for reading, read X bytes, save to write buffer, and enable write event on epoll for socket, go back to 3
   4. If event on normal socket for writing, write bytes from buffer to network, disable write event if write buffer is empty, go back to 3.
   5. If an error occurs remove the socket from epoll
4. There is no fourth step ... the program should loop forever.

很好地解释: https://medium.com/@copyconstruct/the-method-to-epolls-madness-d9d2d6378642