http://blog.csdn.net/lianghe_work/article/details/46519633
与多线程、多进程相比,I/O复用最大的优势是系统开销小,系统不需要建立新的进程或者线程,也不必维护这些线程和进程。
代码示例:
[csharp] view plain copy
- #include <stdio.h>
- #include <unistd.h>
- #include <stdlib.h>
- #include <errno.h>
- #include <string.h>
- #include <sys/socket.h>
- #include <sys/types.h>
- #include <netinet/in.h>
- #include <arpa/inet.h>
- #include <sys/select.h>
- #define SERV_PORT 8080
- #define LIST 20 //服务器最大接受连接
- #define MAX_FD 10 //FD_SET支持描述符数量
- int main(int argc, char *argv[])
- {
- int sockfd;
- int err;
- int i;
- int connfd;
- int fd_all[MAX_FD]; //保存所有描述符,用于select调用后,判断哪个可读
- //下面两个备份原因是select调用后,会发生变化,再次调用select前,需要重新赋值
- fd_set fd_read; //FD_SET数据备份
- fd_set fd_select; //用于select
- struct timeval timeout; //超时时间备份
- struct timeval timeout_select; //用于select
- struct sockaddr_in serv_addr; //服务器地址
- struct sockaddr_in cli_addr; //客户端地址
- socklen_t serv_len;
- socklen_t cli_len;
- //超时时间设置
- timeout.tv_sec = 10;
- timeout.tv_usec = 0;
- //创建TCP套接字
- sockfd = socket(AF_INET, SOCK_STREAM, 0);
- if(sockfd < 0)
- {
- perror("fail to socket");
- exit(1);
- }
- // 配置本地地址
- memset(&serv_addr, 0, sizeof(serv_addr));
- serv_addr.sin_family = AF_INET; // ipv4
- serv_addr.sin_port = htons(SERV_PORT); // 端口, 8080
- serv_addr.sin_addr.s_addr = htonl(INADDR_ANY); // ip
- serv_len = sizeof(serv_addr);
- // 绑定
- err = bind(sockfd, (struct sockaddr *)&serv_addr, serv_len);
- if(err < 0)
- {
- perror("fail to bind");
- exit(1);
- }
- // 监听
- err = listen(sockfd, LIST);
- if(err < 0)
- {
- perror("fail to listen");
- exit(1);
- }
- //初始化fd_all数组
- memset(fd_all, -1, sizeof(fd_all));
- fd_all[0] = sockfd; //第一个为监听套接字
- FD_ZERO(&fd_read); // 清空
- FD_SET(sockfd, &fd_read); //将监听套接字加入fd_read
- int maxfd = fd_all[0]; //监听的最大套接字
- while(1){
- // 每次都需要重新赋值,fd_select,timeout_select每次都会变
- fd_select = fd_read;
- timeout_select = timeout;
- // 检测监听套接字是否可读,没有可读,此函数会阻塞
- // 只要有客户连接,或断开连接,select()都会往下执行
- err = select(maxfd+1, &fd_select, NULL, NULL, NULL);
- //err = select(maxfd+1, &fd_select, NULL, NULL, (struct timeval *)&timeout_select);
- if(err < 0)
- {
- perror("fail to select");
- exit(1);
- }
- if(err == 0){
- printf("timeout\n");
- }
- // 检测监听套接字是否可读
- if( FD_ISSET(sockfd, &fd_select) ){//可读,证明有新客户端连接服务器
- cli_len = sizeof(cli_addr);
- // 取出已经完成的连接
- connfd = accept(sockfd, (struct sockaddr *)&cli_addr, &cli_len);
- if(connfd < 0)
- {
- perror("fail to accept");
- exit(1);
- }
- // 打印客户端的 ip 和端口
- char cli_ip[INET_ADDRSTRLEN] = {0};
- inet_ntop(AF_INET, &cli_addr.sin_addr, cli_ip, INET_ADDRSTRLEN);
- printf("----------------------------------------------\n");
- printf("client ip=%s,port=%d\n", cli_ip,ntohs(cli_addr.sin_port));
- // 将新连接套接字加入 fd_all 及 fd_read
- for(i=0; i < MAX_FD; i++){
- if(fd_all[i] != -1){
- continue;
- }else{
- fd_all[i] = connfd;
- printf("client fd_all[%d] join\n", i);
- break;
- }
- }
- FD_SET(connfd, &fd_read);
- if(maxfd < connfd)
- {
- maxfd = connfd; //更新maxfd
- }
- }
- //从1开始查看连接套接字是否可读,因为上面已经处理过0(sockfd)
- for(i=1; i < maxfd; i++){
- if(FD_ISSET(fd_all[i], &fd_select)){
- printf("fd_all[%d] is ok\n", i);
- char buf[1024]={0}; //读写缓冲区
- int num = read(fd_all[i], buf, 1024);
- if(num > 0){
- //收到 客户端数据并打印
- printf("receive buf from client fd_all[%d] is: %s\n", i, buf);
- //回复客户端
- num = write(fd_all[i], buf, num);
- if(num < 0){
- perror("fail to write ");
- exit(1);
- }else{
- //printf("send reply\n");
- }
- }
- else if(0 == num){ // 客户端断开时
- //客户端退出,关闭套接字,并从监听集合清除
- printf("client:fd_all[%d] exit\n", i);
- FD_CLR(fd_all[i], &fd_read);
- close(fd_all[i]);
- fd_all[i] = -1;
- continue;
- }
- }else {
- //printf("no data\n");
- }
- }
- }
- return 0;
- }
运行结果: