IO多路复用之epoll

- 日理万妓 2024-04-17 23:04 71阅读 0赞

\#include <sys/epoll.h>

int epoll\_ctl(int epfd, int op, int fd, struct epoll\_event \*event);

epoll事件注册函数，

第一个参数epfd: 是函数返回值，

第二个参数op: 表示动作,用三个宏来表示：即

**①，EPOLL\_CTL\_ADD；注册新的事件到epfd中**

**②，EPOLL\_CTL\_MOD；修改已经注册的fd的监听事件**

**③，EPOLL\_CTL\_DEL。从epfd中删除fd的事件**

第三个参数fd: 要监听事件的fd

第三个参数epoll\_event:  ，结构：

** struct epoll\_event \{  
        uint32\_t     events;      /\* Epoll events \*/  
        epoll\_data\_t data;        /\* User data variable \*/  
 \};**

**events可以是：**

EPOLLIN：对应的描述符可以读，  
       EPOLLOUT：对应的描述符可以写  
       EPOLLRDHUP (since Linux 2.6.17)，socket流连接断开，边缘触发，对端连接断开触发，2,6,16之前对端正常关闭：EPOLLIN  
       EPOLLPRI：紧急？数据可读  
       EPOLLERR：描述符发生错误  
       EPOLLHUP：描述符挂起  
       EPOLLET：设置为边缘触发还是水平触发，默认水平触发  
       EPOLLONESHOT (since Linux 2.6.2)

DESCRIPTION  
       This system call performs control operations on the epoll instance referred to by the file descriptor epfd.  It requests that the operation op be performed for the target file descriptor, fd.  
  
       Valid values for the op argument are :  
        **EPOLL\_CTL\_ADD**  
              Register the target file descriptor fd on the epoll instance referred to by the file descriptor epfd and associate the event event with the internal file linked to fd.  
        **EPOLL\_CTL\_MOD**  
              Change the event event associated with the target file descriptor fd.  
    **   EPOLL\_CTL\_DEL**  
              Remove (deregister) the target file descriptor fd from the epoll instance referred to by epfd.  The event is ignored and can be NULL (but see BUGS below)  
  
       The event argument describes the object linked to the file descriptor fd.  The struct epoll\_event is defined as :  
           ** typedef union epoll\_data \{  
               void        \*ptr;  
               int          fd;  
               uint32\_t     u32;  
               uint64\_t     u64;  
           \} epoll\_data\_t;  
  
  
           struct epoll\_event \{  
               uint32\_t     events;      /\* Epoll events \*/  
               epoll\_data\_t data;        /\* User data variable \*/  
           \};**  
  
  
       The events member is a bit set composed using the following available event types:  
       ** EPOLLIN**  
              The associated file is available for read(2) operations.  
     **   EPOLLOUT**  
              The associated file is available for write(2) operations.  
**       EPOLLRDHUP** (since Linux 2.6.17)  
              Stream socket peer closed connection, or shut down writing half of connection.  (This flag is especially useful for writing simple code to detect peer shutdown when using Edge Triggered monitoring.)  
        **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 necessary 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 necessary 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 rearm the file descriptor with a new event mask.  
**RETURN VALUE**  
       When successful, epoll\_ctl() returns zero.  When an error occurs, epoll\_ctl() returns -1 and errno is set appropriately.\\  
**ERRORS  
       EBADF**  epfd or fd is not a valid file descriptor.\\  
      ** EEXIST** op was EPOLL\_CTL\_ADD, and the supplied file descriptor fd is already registered with this epoll instance.

** EINVAL** epfd is not an epoll file descriptor, or fd is the same as epfd, or the requested operation op is not supported by this interface.

**ENOENT** op was EPOLL\_CTL\_MOD or EPOLL\_CTL\_DEL, and fd is not registered with this epoll instance.  
       **ENOMEM** There was insufficient memory to handle the requested op control operation.  
      ** ENOSPC** The limit imposed by /proc/sys/fs/epoll/max\_user\_watches was encountered while trying to register (EPOLL\_CTL\_ADD) a new file descriptor on an epoll instance.  See epoll(7) for further details.  
      ** EPERM**  The target file fd does not support epoll.  
**VERSIONS**  
       epoll\_ctl() was added to the kernel in version 2.6.  
**CONFORMING TO**  
       epoll\_ctl() is Linux-specific.  Library support is provided in glibc starting with version 2.3.2.  
**NOTES**  
       The epoll interface supports all file descriptors that support poll(2).  
**BUGS**  
       In  kernel versions before 2.6.9, the EPOLL\_CTL\_DEL operation required a non-NULL pointer in event, even though this argument is ignored.  Since Linux 2.6.9, event can be specified as NULL when using EPOLL\_CTL\_DEL.  Applica鈥\[m  
       tions that need to be portable to kernels before 2.6.9 should specify a non-NULL pointer in event.  
**SEE ALSO**  
       epoll\_create(2), epoll\_wait(2), poll(2), epoll(7)  
**COLOPHON**  
       This page is part of release 3.35 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.