linux - 是否有必要在关闭之前从 epoll 中注销套接字？

Question

假设以下代码，其中“sock”是 TCP 套接字的句柄，该套接字先前已使用 epfd 指定的 epoll 文件描述符注册。

epoll_ctl(epfd, EPOLL_CTL_DEL, sock, &ev);
close(sock);

如果套接字随后要关闭，是否仍然需要调用 epoll_ctl？或者套接字是否因关闭而隐式注销？

Answer 1

来自man page :

Q6 Will closing a file descriptor cause it to be removed from all epoll sets automatically?

A6 Yes, but be aware of the following point. A file descriptor is a reference to an open file description (see open(2)). Whenever a descriptor is duplicated via dup(2), dup2(2), fcntl(2) F_DUPFD, or fork(2), a new file descriptor referring to the same open file description is created. An open file description continues to exist until all file descriptors referring to it have been closed. A file descriptor is removed from an epoll set only after all the file descriptors referring to the underlying open file description have been closed (or before if the descriptor is explicitly removed using epoll_ctl(2) EPOLL_CTL_DEL). This means that even after a file descriptor that is part of an epoll set has been closed, events may be reported for that file descriptor if other file descriptors referring to the same underlying file description remain open.