两点优化：
（1）SOCK_NONBLOCK设置非阻塞代替非阻塞函数。
（2）将监听listenfd 的判断放在了else if(evs[ii].events & (EPOLLIN | EPOLLPRI))下面，因为listenfd的事件一定是读事件。
// 演示采用epoll模型实现网络通讯的服务端#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/fcntl.h>
#include <sys/epoll.h>
#include <netinet/tcp.h>int main (int argc, char *argv[])
{if(argc != 3) {printf("usage:./tcpepoll ip port\nexample:./tcpepoll 192.168.102.131 5085\n\n"); return -1;}int listenfd = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);if(listenfd < 0) {perror("socket() failed"); return -1; };int opt = 1;setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, static_cast<socklen_t>(sizeof opt));setsockopt(listenfd, SOL_SOCKET, TCP_NODELAY, &opt, static_cast<socklen_t>(sizeof opt));setsockopt(listenfd, SOL_SOCKET, SO_REUSEPORT, &opt, static_cast<socklen_t>(sizeof opt));setsockopt(listenfd, SOL_SOCKET, SO_KEEPALIVE, &opt, static_cast<socklen_t>(sizeof opt));struct sockaddr_in servaddr;servaddr.sin_family = AF_INET;servaddr.sin_addr.s_addr = inet_addr(argv[1]);servaddr.sin_port = htons(atoi(argv[2]));if(bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0) {perror("bind() failed"); close(listenfd); return -1; }if(listen(listenfd, 128) != 0) {perror("listen() failed"); close(listenfd); return -1; };int epollfd = epoll_create(1);struct epoll_event ev;ev.data.fd = listenfd;ev.events = EPOLLIN;epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev);struct epoll_event evs[10];while(true){int infds = epoll_wait(epollfd, evs, 10, -1);if(infds < 0) {perror("epoll_wait() failed"); break; }if(infds == 0) {printf("epoll_wait() timeout.\n"); continue; }for(int ii = 0; ii < infds; ii ++ ){if(evs[ii].events & EPOLLRDHUP) // 对方关闭{printf("client(eventfd = %d) disconnected.\n", evs[ii].data.fd); close(evs[ii].data.fd); }else if(evs[ii].events & (EPOLLIN | EPOLLPRI)) // 接收缓冲区中有数据可以读{if(evs[ii].data.fd == listenfd) // 如果是listenfd有事件，表示有新的客户端连上来{struct sockaddr_in clientaddr;socklen_t len = sizeof(clientaddr);int clientfd = accept4(listenfd, (struct sockaddr*)&clientaddr, &len, SOCK_NONBLOCK);printf("accept client (fd = %d, ip = %s, port = %d)ok.\n", clientfd, inet_ntoa(clientaddr.sin_addr), ntohs(clientaddr.sin_port));ev.data.fd = clientfd;ev.events = EPOLLIN | EPOLLET;epoll_ctl(epollfd, EPOLL_CTL_ADD, clientfd, &ev);}else // 如果是客户端连接的fd有事件{char buffer[1024];while(true){bzero(&buffer, sizeof(buffer));ssize_t nread = read(evs[ii].data.fd, buffer, sizeof(buffer));if(nread > 0) {printf("recv(eventfd = %d):%s\n", evs[ii].data.fd, buffer);send(evs[ii].data.fd, buffer, strlen(buffer), 0);}else if(nread == -1 && errno == EINTR) {continue; }else if(nread == -1 && (errno == EAGAIN || errno == EWOULDBLOCK)) {break; }else if(nread == 0){printf("client(eventfd = %d) disconnected.\n", evs[ii].data.fd);close(evs[ii].data.fd); }}}}else if(evs[ii].events & EPOLLOUT) {} // 有数据需要写else // 其他事件都视为错误{printf("client(eventfd = %d) error.\n", evs[ii].data.fd);close(evs[ii].data.fd);}}}return 0;
}
)
