接着上文，接下来将演示一个TCP回射程序，源代码来自于该博文，在这里将其进行了整合，突出select、poll和epoll不同方法之间的比较，但是代码的结构相同，为了突出方法之间的差别，可能有的代码改动的并不合理，实际中使用并非这么写。
程序逻辑
该程序的主要逻辑如下：
服务器： 1. 开启服务器套接字 2. 将服务器套接字加入要监听的集合中（select的fd_set、poll的pollfd、epoll调用epoll_ctl） 3. 进入循环，调用IO多路复用的API函数（select/poll/epoll_create），如果有事件产生： 3.1. 服务器套接字产生的事件，添加新的客户端到监听集合中 3.2. 客户端套接字产生的事件，读取数据，并立马回传给客户端 客户端： 1. 开启客户端套接字 2. 将客户端套接字和标准输入文件描述符加入要监听的集合中（select的fd_set、poll的pollfd、epoll调用epoll_ctl） 3. 进入循环，调用IO多路复用的API函数（select/poll/epoll_create），如果有事件产生： 3.1. 客户端套接字产生的事件，则读取数据，将其输出到控制台 3.2. 标准输入文件描述符产生的事件，则读取数据，将其通过客户端套接字传给服务器
multiplexing.h
具体代码如下，首先是头文件
//multiplexing.h#ifndef MULTIPLEXING_H#define MULTIPLEXING_H#include#include #include #include #include #include #include #include #include #include #include #include #include using namespace std;#define MAXLINE 1024class Multiplexing {protected: static const int DEFAULT_IO_MAX = 10; //默认的最大文件描述符 static const int INFTIM = -1; int io_max; //记录最大文件描述符 int listenfd; //监听句柄public: Multiplexing() { this->io_max = DEFAULT_IO_MAX; } Multiplexing(int max, int listenfd) { this->io_max = max; this->listenfd = listenfd; } ~Multiplexing() {} virtual void server_do_multiplexing() = 0; //服务端io多路复用 virtual void client_do_multiplexing() = 0; //客户端io多路复用 virtual void handle_client_msg() = 0; //处理客户端消息 virtual bool accept_client_proc() = 0; //接收客户端连接 virtual bool add_event(int confd, int event) = 0; virtual int wait_event() = 0; // 等待事件};//-----------------select-------------------------class MySelect : public Multiplexing {private: fd_set* allfds; //句柄集合 int* clifds; //客户端集合 int maxfd; //记录句柄的最大值 int cli_cnt; //客户端个数public: MySelect() : Multiplexing() { allfds = NULL; clifds = NULL; maxfd = 0; cli_cnt = 0; } MySelect(int max, int listenfd); ~MySelect() { if (allfds) { delete allfds; allfds = NULL; } if (clifds) { delete clifds; clifds = NULL; } } void server_do_multiplexing(); void client_do_multiplexing(); void handle_client_msg(); bool accept_client_proc(); bool add_event(int confd, int event); bool init_event(); //每次调用select前都要重新设置文件描述符 int wait_event(); // 等待事件};//-----------------poll-------------------------typedef struct pollfd Pollfd;class MyPoll : public Multiplexing {private: Pollfd* clientfds; //poll中使用pollfd结构体指定一个被监视的文件描述符 int max_index; //记录当前clientfds数组中使用的最大下标public: MyPoll() : Multiplexing() { clientfds = NULL; max_index = -1; } MyPoll(int max, int listenfd); ~MyPoll() { if (clientfds) { delete clientfds; clientfds = NULL; } } void server_do_multiplexing(); void client_do_multiplexing(); void handle_client_msg(); bool accept_client_proc(); bool add_event(int confd, int event); int wait_event(); // 等待事件};//-----------------epoll-------------------------typedef struct epoll_event Epoll_event;class MyEpoll : public Multiplexing {private: int epollfd; //epoll的句柄，用来管理多个文件描述符 Epoll_event *events; //事件数组 int nready; //在handle_client_msg函数中用到，传给handle_client_msg函数的当前事件的个数public: MyEpoll() : Multiplexing() { events = NULL; epollfd = -1; } MyEpoll(int max, int listenfd); ~MyEpoll() { if (events) { delete events; events = NULL; } } void server_do_multiplexing(); void client_do_multiplexing(); void handle_client_msg(); bool accept_client_proc(); bool add_event(int confd, int event); bool delete_event(int confd, int event); int wait_event(); // 等待事件};#endif // !MULTIPLEXING_H
multiplexing.cpp
然后是函数的实现，从各个函数的实现可以看到select、poll、epoll在使用过程中的区别，具体看代码注释
//multiplexing.cpp#include "multiplexing.h"//--------------------------select------------------MySelect::MySelect(int max, int listenfd) : Multiplexing(max, listenfd) { this->allfds = new fd_set[this->io_max]; this->clifds = new int[this->io_max]; if (NULL == this->allfds || NULL == this->clifds) { perror("initialization failed!"); exit(-1); } this->cli_cnt = 0; this->maxfd = 0; //初始化客户连接描述符 int i; for (i = 0; i < io_max; i++) { this->clifds[i] = -1; }}void MySelect::server_do_multiplexing() { int nready = 0; int i = 0; while (1) { //重新初始化fd_set集合 -- 这里与poll不同 init_event(); /*开始轮询接收处理服务端和客户端套接字*/ nready = wait_event(); if (-1 == nready) return; if (0 == nready) continue; if (FD_ISSET(this->listenfd, this->allfds)) { /*监听客户端请求*/ if (!accept_client_proc()) //处理连接请求 continue; if (--nready <= 0) //说明此时产生的事件个数小于等于1，所以不必再处理下面的客户连接信息 continue; } /*接受处理客户端消息*/ handle_client_msg(); }}void MySelect::client_do_multiplexing() { char sendline[MAXLINE], recvline[MAXLINE]; int n; this->maxfd = -1; int nready = -1; if (this->io_max < 2) { perror("please increase the max number of io!"); exit(1); } //添加连接描述符 if (!add_event(this->listenfd, -1)) { perror("add event error!"); exit(1); } //添加标准输入描述符 if (!add_event(STDIN_FILENO, -1)) { perror("add event error!"); exit(1); } while (1) { //重新初始化fd_set集合 -- 这里与poll不同 init_event(); //等待事件产生 nready = wait_event(); if (-1 == nready) return; if (0 == nready) continue; //是否有客户信息准备好 if (FD_ISSET(this->listenfd, this->allfds)) { n = read(this->listenfd, recvline, MAXLINE); if (n <= 0) { fprintf(stderr, "client: server is closed.\n"); close(this->listenfd); return; } write(STDOUT_FILENO, recvline, n); } //测试标准输入是否准备好 if (FD_ISSET(STDIN_FILENO, this->allfds)) { n = read(STDIN_FILENO, sendline, MAXLINE); if (n <= 0) { shutdown(this->listenfd, SHUT_WR); continue; } write(this->listenfd, sendline, n); } }}bool MySelect::init_event() { FD_ZERO(this->allfds); //重新设置文件描述符 /*添加监听套接字*/ FD_SET(this->listenfd, this->allfds); this->maxfd = this->listenfd; int i; int clifd = -1; /*添加客户端套接字*/ for (i = 0; i < this->cli_cnt; i++) { clifd = this->clifds[i]; /*去除无效的客户端句柄*/ if (clifd != -1) { FD_SET(clifd, this->allfds); } this->maxfd = (clifd > this->maxfd ? clifd : this->maxfd); }}bool MySelect::accept_client_proc() { struct sockaddr_in cliaddr; socklen_t cliaddrlen; cliaddrlen = sizeof(cliaddr); int connfd; //接受新的连接 if ((connfd = accept(this->listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen)) == -1) { if (errno == EINTR) return false; else { perror("accept error:"); exit(1); } } fprintf(stdout, "accept a new client: %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port); return add_event(connfd, -1); //添加新的描述符}bool MySelect::add_event(int connfd, int event) { //在select中event并没有作用 //将新的连接描述符添加到数组中 int i = 0; for (i = 0; i < io_max; i++) { if (this->clifds[i] < 0) { this->clifds[i] = connfd; this->cli_cnt++; break; } } if (i == io_max) { fprintf(stderr, "too many clients.\n"); return false; } //将新的描述符添加到读描述符集合中 FD_SET(connfd, this->allfds); if (connfd > this->maxfd) this->maxfd = connfd; return true;}void MySelect::handle_client_msg() { int i = 0, n = 0; int clifd; char buf[MAXLINE]; memset(buf, 0, MAXLINE); //处理信息 for (i = 0; i <= this->cli_cnt; i++) { clifd = this->clifds[i]; if (clifd < 0) { continue; } /*判断客户端套接字是否有数据*/ if (FD_ISSET(clifd, this->allfds)) { //接收客户端发送的信息 n = read(clifd, buf, MAXLINE); if (n <= 0) { /*n==0表示读取完成，客户都关闭套接字*/ FD_CLR(clifd, this->allfds); close(clifd); this->clifds[i] = -1; continue; } //回写数据 printf("recv buf is :%s\n", buf); write(clifd, buf, n); return; } }}int MySelect::wait_event() { struct timeval tv; /*每次调用select前都要重新设置文件描述符和时间，因为事件发生后，文件描述符和时间都被内核修改啦*/ tv.tv_sec = 30; tv.tv_usec = 0; /*开始轮询接收处理服务端和客户端套接字*/ int nready = select(this->maxfd + 1, this->allfds, NULL, NULL, &tv); if (nready == -1) { fprintf(stderr, "select error:%s.\n", strerror(errno)); } if (nready == 0) { fprintf(stdout, "select is timeout.\n"); } return nready;}//-----------------poll-------------------------MyPoll::MyPoll(int max, int listenfd) : Multiplexing(max, listenfd) { this->clientfds = new Pollfd[this->io_max]; //初始化客户连接描述符 int i; for (i = 0; i < io_max; i++) { this->clientfds[i].fd = -1; } this->max_index = -1;}void MyPoll::server_do_multiplexing() { int sockfd; int i; int nready; this->max_index = -1; //注意：需要将监听描述符添加在第一个位置 if (!add_event(this->listenfd, POLLIN)) { perror("add listen event error!"); return; } //循环处理 while (1) { //等待事件，获取可用描述符的个数 nready = wait_event(); if (nready == -1) { return; } if (nready == 0) { continue; } //测试监听描述符是否准备好 if (this->clientfds[0].revents & POLLIN) { if (!accept_client_proc()) //处理连接请求 continue; if (--nready <= 0) //说明此时产生的事件个数小于等于1，所以不必再处理下面的客户连接信息 continue; } //处理客户连接 handle_client_msg(); }}void MyPoll::client_do_multiplexing() { char sendline[MAXLINE], recvline[MAXLINE]; int n; this->max_index = -1; int nready = -1; if (this->io_max < 2) { perror("please increase the max number of io!"); exit(1); } //添加连接描述符 if (!add_event(this->listenfd, POLLIN)) { perror("add event error!"); exit(1); } //添加标准输入描述符 if (!add_event(STDIN_FILENO, POLLIN)) { perror("add event error!"); exit(1); } while (1) { //等待事件产生 nready = wait_event(); if (-1 == nready) return; if (0 == nready) continue; //是否有客户信息准备好 if (this->clientfds[0].revents & POLLIN) { n = read(this->listenfd, recvline, MAXLINE); if (n <= 0) { fprintf(stderr, "client: server is closed.\n"); close(this->listenfd); return; } write(STDOUT_FILENO, recvline, n); } //测试标准输入是否准备好 if (this->clientfds[1].revents & POLLIN) { n = read(STDIN_FILENO, sendline, MAXLINE); if (n <= 0) { shutdown(this->listenfd, SHUT_WR); continue; } write(this->listenfd, sendline, n); } }}bool MyPoll::accept_client_proc() { struct sockaddr_in cliaddr; socklen_t cliaddrlen; cliaddrlen = sizeof(cliaddr); int connfd; //接受新的连接 if ((connfd = accept(this->listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen)) == -1) { if (errno == EINTR) return false; else { perror("accept error:"); exit(1); } } fprintf(stdout, "accept a new client: %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port); return add_event(connfd, POLLIN); //添加新的描述符}bool MyPoll::add_event(int connfd, int event) { //将新的连接描述符添加到数组中 int i; for (i = 0; i < io_max; i++) { if (this->clientfds[i].fd < 0) { this->clientfds[i].fd = connfd; break; } } if (i == io_max) { fprintf(stderr, "too many clients.\n"); return false; } //将新的描述符添加到读描述符集合中 this->clientfds[i].events = event; if (i > this->max_index) this->max_index = i; return true;}void MyPoll::handle_client_msg() { int i, n; char buf[MAXLINE]; memset(buf, 0, MAXLINE); //处理信息 for (i = 1; i <= this->max_index; i++) { if (this->clientfds[i].fd < 0) continue; //测试客户描述符是否准备好 if (this->clientfds[i].revents & POLLIN) { //接收客户端发送的信息 n = read(this->clientfds[i].fd, buf, MAXLINE); if (n <= 0) { close(this->clientfds[i].fd); this->clientfds[i].fd = -1; continue; } write(STDOUT_FILENO, buf, n); //向客户端发送buf write(this->clientfds[i].fd, buf, n); } }}int MyPoll::wait_event() { /*开始轮询接收处理服务端和客户端套接字*/ int nready = nready = poll(this->clientfds, this->max_index + 1, INFTIM); if (nready == -1) { fprintf(stderr, "poll error:%s.\n", strerror(errno)); } if (nready == 0) { fprintf(stdout, "poll is timeout.\n"); } return nready;}//------------------------epoll---------------------------MyEpoll::MyEpoll(int max, int listenfd) : Multiplexing(max, listenfd) { this->events = new Epoll_event[this->io_max]; //创建一个描述符 this->epollfd = epoll_create(this->io_max);}void MyEpoll::server_do_multiplexing() { int i, fd; int nready; char buf[MAXLINE]; memset(buf, 0, MAXLINE); //添加监听描述符事件 if (!add_event(this->listenfd, EPOLLIN)) { perror("add event error!"); exit(1); } while (1) { //获取已经准备好的描述符事件 nready = wait_event(); this->nready = nready; if (-1 == nready) return; if (0 == nready) continue; //进行遍历 /**这里和poll、select都不同，因为并不能直接判断监听的事件是否产生， 所以需要一个for循环遍历，这个for循环+判断类似于poll中 if (FD_ISSET(this->listenfd, this->allfds))、 select中的if (this->clientfds[0].revents & POLLIN) 这里只是尽量写的跟poll、select中的结构类似， 但是实际代码中，不应该这么写，这么写多加了一个for循环**/ for (i = 0; i < nready; i++) { fd = events[i].data.fd; //根据描述符的类型和事件类型进行处理 if ((fd == this->listenfd) && (events[i].events & EPOLLIN)) { //监听事件 /*监听客户端请求*/ if (!accept_client_proc()) //处理连接请求 continue; //说明此时产生的事件个数小于等于1，所以不必再处理下面的客户连接信息 if (--nready <= 0) continue; } } //处理客户端事件 handle_client_msg(); } close(epollfd);}bool MyEpoll::accept_client_proc() { struct sockaddr_in cliaddr; socklen_t cliaddrlen; cliaddrlen = sizeof(cliaddr); int connfd; //接受新的连接 if ((connfd = accept(this->listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen)) == -1) { if (errno == EINTR) return false; else { perror("accept error:"); exit(1); } } fprintf(stdout, "accept a new client: %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port); return add_event(connfd, EPOLLIN); //添加新的描述符}void MyEpoll::client_do_multiplexing() { char sendline[MAXLINE], recvline[MAXLINE]; int n; int nready = -1; int i, fd; if (this->io_max < 2) { perror("please increase the max number of io!"); exit(1); } //添加连接描述符 if (!add_event(this->listenfd, POLLIN)) { perror("add event error!"); exit(1); } //添加标准输入描述符 if (!add_event(STDIN_FILENO, POLLIN)) { perror("add event error!"); exit(1); } while (1) { //等待事件产生 nready = wait_event(); if (-1 == nready) return; if (0 == nready) continue; for (i = 0; i < nready; i++) { fd = events[i].data.fd; //根据描述符的类型和事件类型进行处理 if ((fd == this->listenfd) && (events[i].events & EPOLLIN)) { //监听事件 n = read(this->listenfd, recvline, MAXLINE); if (n <= 0) { fprintf(stderr, "client: server is closed.\n"); close(this->listenfd); return; } write(STDOUT_FILENO, recvline, n); } else { n = read(STDIN_FILENO, sendline, MAXLINE); if (n <= 0) { shutdown(this->listenfd, SHUT_WR); continue; } write(this->listenfd, sendline, n); } } }}bool MyEpoll::add_event(int connfd, int event) { //将新的描述符添加到读描述符集合中 Epoll_event ev; ev.events = event; ev.data.fd = connfd; return epoll_ctl(this->epollfd, EPOLL_CTL_ADD, connfd, &ev) == 0;}void MyEpoll::handle_client_msg() { int i, fd; char buf[MAXLINE]; memset(buf, 0, MAXLINE); //处理信息 for (i = 0; i <= this->nready; i++) { fd = this->events[i].data.fd; if (fd == this->listenfd) continue; if (events[i].events & EPOLLIN) { int n = read(fd, buf, MAXLINE); if (n <= 0) { perror("read error:"); close(fd); delete_event(fd, EPOLLIN); } else { write(STDOUT_FILENO, buf, n); //向客户端发送buf write(fd, buf, strlen(buf)); } } }}int MyEpoll::wait_event() { /*开始轮询接收处理服务端和客户端套接字*/ int nready = epoll_wait(this->epollfd, this->events, this->io_max, INFTIM);; if (nready == -1) { fprintf(stderr, "poll error:%s.\n", strerror(errno)); } if (nready == 0) { fprintf(stdout, "poll is timeout.\n"); } return nready;}bool MyEpoll::delete_event(int fd, int state) { Epoll_event ev; ev.events = state; ev.data.fd = fd; return epoll_ctl(this->epollfd, EPOLL_CTL_DEL, fd, &ev) == 0;} 服务器代码
#include "multiplexing.h"#define IPADDRESS "127.0.0.1"#define PORT 8787#define LISTENQ 5#define OPEN_MAX 1000//函数声明//创建套接字并进行绑定static int socket_bind(const char* ip, int port);int main(int argc, char *argv[]) { int listenfd = socket_bind(IPADDRESS, PORT); if (listenfd < 0) { perror("socket bind error"); return 0; } listen(listenfd, LISTENQ); // 改动此处，调用不同的IO复用函数 MySelect mltp(OPEN_MAX, listenfd); //MyPoll mltp(OPEN_MAX, listenfd); //MyEpoll mltp(OPEN_MAX, listenfd); mltp.server_do_multiplexing(); //处理服务端 return 0;}static int socket_bind(const char* ip, int port) { int listenfd; struct sockaddr_in servaddr; listenfd = socket(AF_INET, SOCK_STREAM, 0); if (listenfd == -1) { perror("socket error:"); exit(1); } bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; inet_pton(AF_INET, ip, &servaddr.sin_addr); servaddr.sin_port = htons(port); if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) == -1) { perror("bind error: "); exit(1); } return listenfd;} 客户端代码
#include "multiplexing.h"#define MAXLINE 1024#define IPADDRESS "127.0.0.1"#define SERV_PORT 8787static void handle_connection(int sockfd);int main(int argc, char *argv[]) { int sockfd; struct sockaddr_in servaddr; sockfd = socket(AF_INET, SOCK_STREAM, 0); bzero(&servaddr, sizeof(servaddr)); servaddr.sin_family = AF_INET; servaddr.sin_port = htons(SERV_PORT); inet_pton(AF_INET, IPADDRESS, &servaddr.sin_addr); connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)); // 改动此处，调用不同的IO复用函数 MySelect mltp(2, sockfd); //MyPoll mltp(2, sockfd); //MyEpoll mltp(2, sockfd); poll.client_do_multiplexing(); // 处理客户端 return 0;} 运行结果
服务端：
](https://image-static.segmentfault.com/407/048/407048720-5b9b5f6be5b89_articlex "")
客户端：
](https://image-static.segmentfault.com/181/784/1817842921-5b9b5f7b8a046_articlex "")
完整代码可以访问笔者github：
参考资料
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