man epoll指南節選

在linux終端通過命令：
man epoll
可查看epoll的編程指南。

其中以下內容值得重點學習。
Example for suggested usage
While the usage of epoll when employed as a level-triggered interface does have the same semantics as poll(2), the edge-triggered usage requires more clarification to avoid stalls in the application event loop.In this example, listener is a nonblocking socket on which listen(2) has been called.  

The function do_use_fd() uses the new ready file descriptor until EAGAIN is returned by either read(2) or write(2).  An event-driven state machine application should, after having received EAGAIN, record its current state so that at the next call to do_use_fd() it will continue to read(2) or write(2) from where it stopped before.

#define MAX_EVENTS 10

void epoll_func(void)
{
	struct epoll_event ev, events[MAX_EVENTS];
	int listen_sock, conn_sock, nfds, epollfd;

	/* Code to set up listening socket, 'listen_sock',
	(socket(), bind(), listen()) omitted */

	epollfd = epoll_create1(0);
	if (epollfd == -1) {
		perror("epoll_create1");
		exit(EXIT_FAILURE);
	}

	ev.events = EPOLLIN;
	ev.data.fd = listen_sock;
	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, listen_sock, &ev) == -1) {
		perror("epoll_ctl: listen_sock");
		exit(EXIT_FAILURE);
	}

	for (;;) {
		nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
		if (nfds == -1) {
			perror("epoll_wait");
			exit(EXIT_FAILURE);
		}

		for (n = 0; n < nfds; ++n) {
			if (events[n].data.fd == listen_sock) {
				conn_sock = accept(listen_sock, (struct sockaddr *) &local, &addrlen);
				if (conn_sock == -1) {
					perror("accept");
					exit(EXIT_FAILURE);
				}
				setnonblocking(conn_sock);
				ev.events = EPOLLIN | EPOLLET;
				ev.data.fd = conn_sock;
				if (epoll_ctl(epollfd, EPOLL_CTL_ADD, conn_sock, &ev) == -1) {
					perror("epoll_ctl: conn_sock");
					exit(EXIT_FAILURE);
				}
			} else {
				do_use_fd(events[n].data.fd);
			}
		}
	}
}

When used as an edge-triggered interface, for performance reasons, it is possible to add the file descriptor inside the epoll interface (EPOLL_CTL_ADD) once by specifying (EPOLLIN|EPOLLOUT).  This allows you to  avoid continuously switching between EPOLLIN and EPOLLOUT calling epoll_ctl(2) with EPOLL_CTL_MOD.