网络编程--服务器编程模型

本文通过一个简单的例子，介绍网络服务器编程模型
服务器接受客户端连接请求，回显客户端发过来的数据，发送当前时间给客户端

所有源码可打包下载：
http://download.csdn.net/detail/yfkiss/4318990

客户端请求相关代码：

 //和服务器建立连接
 if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1)
 {
         perror("connect");
         exit(1);
 }

 //向服务器发送请求
 if(send(sockfd,buf,strlen(buf),0)==-1)
 {
         perror("send");
         exit(1);
 }
 memset(buf,0,sizeof(buf));

 //接受从服务器返回的信息
 if((numbytes = recv(sockfd,buf,100,0))==-1)
 {
         perror("recv");
         exit(1);
 }
 else
 {
         printf("Time: %s\n", buf);
 }

简单服务器模型

服务器进程接受连接，处理请求，然后等待下一个连接，如图：

核心代码：

        //等待连接
 while(1)
 {
     struct sockaddr cliaddr;
     sin_size = sizeof(struct sockaddr);

     //接受连接
     if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1)
     {
         perror("accept");
         return -1;
     }

     char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
     getnameinfo(&cliaddr, sizeof(cliaddr), hbuf, sizeof hbuf, sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV);
     printf("Accepted connection: host=%s, port=%s\n", hbuf, sbuf);

     //读取客户端发来的信息
     memset(buff,0,sizeof(buff));
     if((numbytes = recv(new_fd,buff,sizeof(buff),0))==-1)
     {
         perror("recv");
         return -1;
     }

     //获取系统时间
     time_t now = time(0);
     sprintf(buff, "Server Time is : %s", ctime(&now));

     //将从客户端接收到的信息再发回客户端
     if(send(new_fd,buff,strlen(buff),0)==-1)
     {
         perror("send");
     }

     //关闭连接
     close(new_fd);
 }

多进程模型

服务器进程接受连接，fork一个子进程为客户服务，然后等待下一个连接。
多进程模型适用于单个客户服务需要消耗较多的 CPU 资源，例如需要进行大规模或长时间的数据运算或文件访问。多进程模型具有较好的安全性。
如图：

核心代码：

     //等待连接
     while(1)
     {
         struct sockaddr cliaddr;
         sin_size = sizeof(struct sockaddr);

         //接受连接
         if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1)
         {
             perror("accept");
             return -1;
         }

         char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
         getnameinfo(&cliaddr, sizeof(cliaddr), hbuf, sizeof hbuf, sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV);
         printf("Accepted connection: host=%s, port=%s\n", hbuf, sbuf);

                 //fork子进程处理请求
         if(!fork())
         {
             process(new_fd);

             //关闭连接
             close(new_fd);
             return 0;
         }

     }
     close(sockfd);
 }

多线程模型

和多进程模型类似，服务器进程接受连接，新建一个线程为客户服务，然后等待下一个连接
和多进程相比，由于进程消耗的资源比线程大的多，因此，在需要为较多客户端服务的时候，优先使用多线程。
如图：

代码：

 void* process(void* arg)
 {
     int new_fd = *(int*)arg;
     char buff[1024];
     int numbytes;

     //读取客户端发来的信息
     memset(buff,0,sizeof(buff));
     if((numbytes = recv(new_fd,buff,sizeof(buff),0))==-1)
     {
         perror("recv");
         return NULL;
     }


     //获取系统时间
     time_t now = time(0);
     sprintf(buff, "Server Time is : %s", ctime(&now));

     //将从客户端接收到的信息再发回客户端
     if(send(new_fd,buff,strlen(buff),0)==-1)
     {
         perror("send");
         return NULL;
     }

     close(new_fd);
         pthread_exit(NULL);
     return NULL;
 }

 int main()
 {
     ......

     //等待连接
     while(1)
     {
         struct sockaddr cliaddr;
         sin_size = sizeof(struct sockaddr);

         //接受连接
         if((new_fd = accept(sockfd, (struct sockaddr *)&cliaddr, (socklen_t*)&sin_size))==-1)
         {
             perror("accept");
             return -1;
         }

         char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
         getnameinfo(&cliaddr, sizeof(cliaddr), hbuf, sizeof hbuf, sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV);
         printf("Accepted connection: host=%s, port=%s\n", hbuf, sbuf);

                 //创建新线程为客户端服务
         if((pthread_create(&thread, NULL, process, (void*)(&new_fd))))
         {
             perror("pthread_create error");
             return 0;
         }
     }
     close(sockfd);
 }

事件驱动模型

多线程模型通过将连接与线程绑定的方式，较好的解决了同一时刻为多个客户提供请求的要求，但是，如果客户请求数成千上万，即使是线程，服务器也无法承受庞大的资源消耗。当然，我们可以通过使用线程池来控制线程数量，减少资源开销，但是，面对大的服务压力，池本身无法增加承载能力。
事件驱动模型使用IO复用（参考网络编程--IO模型示例），在每一个执行周期都会探测一次或一组事件，一个特定的事件会触发某个特定的响应。
相比其他模型，事件驱动模型优点是只用单线程执行，占用资源少，不消耗太多 CPU，同时能够为多客户端提供服务。缺点是程序逻辑复杂，编程复杂性较高。
如图：

核心代码：

 #define MAX_EVENTS 1024

 struct myevent_s
 {
     int fd;
     void (*call_back)(int fd, int events, void *arg);
     int events;
     void *arg;
     int status; // 1: in epoll wait list, 0 not in
     char buff[128]; // recv data buffer
     int len;
     long last_active; // last active time
 };

 int g_epollFd;
 myevent_s g_Events[MAX_EVENTS+1]; // g_Events[MAX_EVENTS] is used by listen fd
 void RecvData(int fd, int events, void *arg);
 void SendData(int fd, int events, void *arg);

 // set event
 void EventSet(myevent_s *ev, int fd, void (*call_back)(int, int, void*), void *arg)
 {
     ev->fd = fd;
     ev->call_back = call_back;
     ev->events = 0;
     ev->arg = arg;
     ev->status = 0;
     ev->len = 0;
     ev->last_active = time(NULL);
 }

 // add/mod an event to epoll
 void EventAdd(int epollFd, int events, myevent_s *ev)
 {
     struct epoll_event epv = {0, {0}};
     int op;
     epv.data.ptr = ev;
     epv.events = ev->events = events;
     if(ev->status == 1){
         op = EPOLL_CTL_MOD;
     }
     else{
         op = EPOLL_CTL_ADD;
         ev->status = 1;
     }
     if(epoll_ctl(epollFd, op, ev->fd, &epv) < 0)
         printf("Event Add failed[fd=%d]\n", ev->fd);
     else
         printf("Event Add OK[fd=%d]\n", ev->fd);
 }

 // delete an event from epoll
 void EventDel(int epollFd, myevent_s *ev)
 {
     struct epoll_event epv = {0, {0}};
     if(ev->status != 1) return;
     epv.data.ptr = ev;
     ev->status = 0;
     epoll_ctl(epollFd, EPOLL_CTL_DEL, ev->fd, &epv);
 }

 // accept new connections from clients
 void AcceptConn(int fd, int events, void *arg)
 {
     struct sockaddr_in sin;
     socklen_t len = sizeof(struct sockaddr_in);
     int nfd, i;
     // accept
     if((nfd = accept(fd, (struct sockaddr*)&sin, &len)) == -1)
     {
         if(errno != EAGAIN && errno != EINTR)
         {
             printf("%s: bad accept", __func__);
         }
         return;
     }
     do
     {
         for(i = 0; i < MAX_EVENTS; i++)
         {
             if(g_Events[i].status == 0)
             {
                 break;
             }
         }
         if(i == MAX_EVENTS)
         {
             printf("%s:max connection limit[%d].", __func__, MAX_EVENTS);
             break;
         }
         // set nonblocking
         if(fcntl(nfd, F_SETFL, O_NONBLOCK) < 0) break;
         // add a read event for receive data
         EventSet(&g_Events[i], nfd, RecvData, &g_Events[i]);
         EventAdd(g_epollFd, EPOLLIN|EPOLLET, &g_Events[i]);
         printf("new conn[%s:%d][time:%d]\n", inet_ntoa(sin.sin_addr), ntohs(sin.sin_port), g_Events[i].last_active);
     }while(0);
 }

 // receive data
 void RecvData(int fd, int events, void *arg)
 {
     struct myevent_s *ev = (struct myevent_s*)arg;
     int len;
     // receive data
     len = recv(fd, ev->buff, sizeof(ev->buff)-1, 0);
     EventDel(g_epollFd, ev);
     if(len > 0)
     {
         ev->len = len;
         ev->buff[len] = '\0';
         printf("C[%d]:%s\n", fd, ev->buff);
         // change to send event
         EventSet(ev, fd, SendData, ev);
         EventAdd(g_epollFd, EPOLLOUT|EPOLLET, ev);
     }
     else if(len == 0)
     {
         close(ev->fd);
         printf("[fd=%d] closed gracefully.\n", fd);
     }
     else
     {
         close(ev->fd);
         printf("recv[fd=%d] error[%d]:%s\n", fd, errno, strerror(errno));
     }
 }

 // send data
 void SendData(int fd, int events, void *arg)
 {
     struct myevent_s *ev = (struct myevent_s*)arg;
     int len;

     time_t now = time(0);
     sprintf(ev->buff, "Server Time is : %s", ctime(&now));
     // send data
     len = send(fd, ev->buff, strlen(ev->buff), 0);
     ev->len = 0;
     EventDel(g_epollFd, ev);
     if(len > 0)
     {
         // change to receive event
         EventSet(ev, fd, RecvData, ev);
         EventAdd(g_epollFd, EPOLLIN|EPOLLET, ev);
     }
     else
     {
         close(ev->fd);
         printf("recv[fd=%d] error[%d]\n", fd, errno);
     }
 }
 void InitListenSocket(int epollFd, short port)
 {
     int listenFd = socket(AF_INET, SOCK_STREAM, 0);
     fcntl(listenFd, F_SETFL, O_NONBLOCK); // set non-blocking
     printf("server listen fd=%d\n", listenFd);
     EventSet(&g_Events[MAX_EVENTS], listenFd, AcceptConn, &g_Events[MAX_EVENTS]);
     // add listen socket
     EventAdd(epollFd, EPOLLIN|EPOLLET, &g_Events[MAX_EVENTS]);
     // bind & listen
     sockaddr_in sin;
     bzero(&sin, sizeof(sin));
     sin.sin_family = AF_INET;
     sin.sin_addr.s_addr = INADDR_ANY;
     sin.sin_port = htons(port);
     bind(listenFd, (const sockaddr*)&sin, sizeof(sin));
     listen(listenFd, 5);
 }

 int main(int argc, char **argv)
 {
     short port = 7092; // default port

     // create epoll
     g_epollFd = epoll_create(MAX_EVENTS);
     if(g_epollFd <= 0) printf("create epoll failed.%d\n", g_epollFd);

     // create & bind listen socket, and add to epoll, set non-blocking
     InitListenSocket(g_epollFd, port);

     // event loop
     struct epoll_event events[MAX_EVENTS];
     printf("server running:port[%d]\n", port);

     int checkPos = 0;
     while(1){
         // a simple timeout check here, every time 100, better to use a mini-heap, and add timer event
         long now = time(NULL);
         for(int i = 0; i < 100; i++, checkPos++) // doesn't check listen fd
         {
             if(checkPos == MAX_EVENTS) checkPos = 0; // recycle
             if(g_Events[checkPos].status != 1) continue;
             long duration = now - g_Events[checkPos].last_active;
             if(duration >= 60) // 60s timeout
             {
                 close(g_Events[checkPos].fd);
                 printf("[fd=%d] timeout[%d--%d].\n", g_Events[checkPos].fd, g_Events[checkPos].last_active, now);
                 EventDel(g_epollFd, &g_Events[checkPos]);
             }
         }
         // wait for events to happen
         int fds = epoll_wait(g_epollFd, events, MAX_EVENTS, 1000);
         if(fds < 0){
             printf("epoll_wait error, exit\n");
             break;
         }
         for(int i = 0; i < fds; i++){
             myevent_s *ev = (struct myevent_s*)events[i].data.ptr;
             if((events[i].events&EPOLLIN)&&(ev->events&EPOLLIN)) // read event
             {
                 ev->call_back(ev->fd, events[i].events, ev->arg);
             }
             if((events[i].events&EPOLLOUT)&&(ev->events&EPOLLOUT)) // write event
             {
                 ev->call_back(ev->fd, events[i].events, ev->arg);
             }
         }
     }
     // free resource
     return 0;
 }

总结：

多进程和多线程适用于小规模，长连接的场景
事件驱动适用于大规模、IO密集、大量慢连接、短连接的场景

reference：
Beyond Apache: Fater Web Servers
高性能并发Web服务器实现核心内幕
使用事件驱动模型实现高效稳定的网络服务器程序
Linux Epoll介绍和程序实例