epoll各事件触发条件（转）

源地址：epoll的各个事件触发条件测试

1、listen fd，有新连接请求，触发EPOLLIN。
2、对端发送普通数据，触发EPOLLIN。
3、带外数据，只触发EPOLLPRI。
4、对端正常关闭（程序里close()，shell下kill或ctr+c），触发EPOLLIN和EPOLLRDHUP，但是不触发EPOLLERR和EPOLLHUP。
    关于这点，以前一直以为会触发EPOLLERR或者EPOLLHUP。
    再man epoll_ctl看下后两个事件的说明，这两个应该是本端（server端）出错才触发的。
5、对端异常断开连接（只测了拔网线），没触发任何事件。

//理解：

EPOLLIN：对端发送数据，只要接收缓冲区没有满，都会触发，不管接收缓冲区内是否上次未读完的信息

EPOLLOUT:（可写，理解的意思是：缓冲区有空间可以写入，epoll通知）发送缓冲区从满到未满（哪怕只剩一个字节没有满），会触发这个事件

附man：
EPOLLIN
              The associated file is available for read(2) operations.
EPOLLOUT
              The associated file is available for write(2) operations.
EPOLLRDHUP
              Stream  socket peer closed connection, or shut down writing half
              of connection.  (This flag is especially useful for writing sim-
              ple code to detect peer shutdown when using Edge Triggered moni-
              toring.)
EPOLLPRI
              There is urgent data available for read(2) operations.
EPOLLERR
              Error condition happened  on  the  associated  file  descriptor.
              epoll_wait(2)  will always wait for this event; it is not neces-
              sary to set it in events.
EPOLLHUP
              Hang  up   happened   on   the   associated   file   descriptor.
              epoll_wait(2)  will always wait for this event; it is not neces-
              sary to set it in events.
EPOLLET
              Sets  the  Edge  Triggered  behavior  for  the  associated  file
              descriptor.   The default behavior for epoll is Level Triggered.
              See epoll(7) for more detailed information about Edge and  Level
              Triggered event distribution architectures.
EPOLLONESHOT (since Linux 2.6.2)
              Sets  the  one-shot behavior for the associated file descriptor.
              This means that after an event is pulled out with  epoll_wait(2)
              the  associated  file  descriptor  is internally disabled and no
              other events will be reported by the epoll interface.  The  user
              must  call  epoll_ctl() with EPOLL_CTL_MOD to re-enable the file
              descriptor with a new event mask.