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：
//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：
//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：
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
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