分类： LINUX
2012-03-04 20:10:43
IO多路复用
与多线程和多进程相比，I/O多路复用的最大优势是系统开销小，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。
主要应用：
（1）客户程序需要同时处理交互式的输入和服务器之间的网络连接
（2）客户端需要对多个网络连接作出反应
（3）TCP服务器需要同时处理多个处于监听状态和多个连接状态的套接字
（4）服务器需要处理多个网络协议的套接字
（5）服务器需要同时处理不同的网络服务和协议
3. IO多路复用模式
4. select()函数
#include
int select(int nfds, fd_set *readfds, fd_set *wtitefds, fd_set *errnofds,
struct timeval *timeout)
注意：描述符不受限与套接字，任何描述符都行
nfds：select()函数监视的描述符数的最大值，一般取监视的描述符数的最大值+1，
其上限设置在sys/types.h中有定义
#define FD_SETSIZE 256
readfds：select()函数监视的可读描述符集合
wtitefds：select()函数监视的可写描述符集合
errnofds：select()函数监视的异常描述符集合
timeout：select()函数监视超时结束时间，取NULL表示永久等待
返回值：返回总的位数这些位对应已准备好的描述符，否则返回-1
相关宏操作：
FD_ZERO(fd_set *fdset)：清空fdset与所有描述符的关系
FD_SET(int fd, d_set * fdset)：建立描述符fd与fdset得关系
FD_CLR(int fd, d_set * fdset)：撤销描述符fd与fdset得关系
FD_ISSET(int fd, d_set * fdset)：检查与fdset联系的描述符fd是否可以读写，返回非零表示可以读写
5. select()函数实现IO多路复用的步骤
（1）清空描述符集合
（2）建立需要监视的描述符与描述符集合的关系
（3）调用select函数
（4）检查监视的描述符判断是否已经准备好
（5）对已经准备好的描述符进程IO操作
6．单线程并发服务器设计实例
功能：
服务器等候客户连接请求，一旦连接成功显示客户地址，接收该客户的名字并显示，然后接收来自用户的信息，每收到一个字符串则显示，并将字符串反转，再将反转的字符串发回客户端。
客户端首先与服务器相连，接着发送客户端名字，然后发送客户信息，接收到服务器信息并显示，之后等待用户输入Crtl+D，就关闭连接并退出。
//server.c
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define PORT 1234 /* Port that will be opened */
#define BACKLOG 5 /* Number of allowed connections */
#define MAXDATASIZE 1000
typedef struct CLIENT{
int fd;
char* name;
struct sockaddr_in addr; /* client's address information */
char* data;
};
void process_cli(CLIENT *client, char* recvbuf, int len);
void savedata(char* recvbuf, int len, char* data);
main()
{
int i, maxi, maxfd,sockfd;
int nready;
ssize_t n;
fd_set rset, allset;
int listenfd, connectfd; /* socket descriptors */
struct sockaddr_in server; /* server's address information */
/* client's information */
CLIENT client[FD_SETSIZE];
char recvbuf[MAXDATASIZE];
socklen_t sin_size;
/* Create TCP socket */
if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
/* handle exception */
perror("Creating socket failed.");
exit(1);
}
int opt = SO_REUSEADDR;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
bzero(&server,sizeof(server));
server.sin_family=AF_INET;
server.sin_port=htons(PORT);
server.sin_addr.s_addr = htonl (INADDR_ANY);
if (bind(listenfd, (struct sockaddr *)&server, sizeof(struct sockaddr)) == -1) {
/* handle exception */
perror("Bind error.");
exit(1);
}
if(listen(listenfd,BACKLOG) == -1){ /* calls listen() */
perror("listen() error\n");
exit(1);
}
sin_size=sizeof(struct sockaddr_in);
/*initialize for select */
maxfd = listenfd;
maxi = -1;
for (i = 0; i < FD_SETSIZE; i++) {
client[i].fd = -1;
}
FD_ZERO(&allset);
FD_SET(listenfd, &allset);
while(1)
{
struct sockaddr_in addr;
rset = allset;
nready = select(maxfd+1, &rset, NULL, NULL, NULL);
if (FD_ISSET(listenfd, &rset)) { /* new client connection */
/* Accept connection */
if ((connectfd = accept(listenfd,(struct sockaddr *)&addr,&sin_size))==-1) {
perror("accept() error\n");
continue;
}
/* Put new fd to client */
for (i = 0; i < FD_SETSIZE; i++)
if (client[i].fd < 0) {
client[i].fd = connectfd; /* save descriptor */
client[i].name = new char[MAXDATASIZE];
client[i].addr = addr;
client[i].data = new char[MAXDATASIZE];
client[i].name[0] = '\0';
client[i].data[0] = '\0';
printf("You got a connection from %s. ",inet_ntoa(client[i].addr.sin_addr) );
break;
}
if (i == FD_SETSIZE) printf("too many clients\n");
FD_SET(connectfd, &allset); /* add new descriptor to set */
if (connectfd > maxfd) maxfd = connectfd;
if (i > maxi) maxi = i;
if (--nready <= 0) continue; /* no more readable descriptors */
}
for (i = 0; i <= maxi; i++) { /* check all clients for data */
if ( (sockfd = client[i].fd) < 0) continue;
if (FD_ISSET(sockfd, &rset)) {
if ( (n = recv(sockfd, recvbuf, MAXDATASIZE,0)) == 0) {
/*connection closed by client */
close(sockfd);
printf("Client( %s ) closed connection. User's data: %s\n",client[i].name,client[i].data);
FD_CLR(sockfd, &allset);
client[i].fd = -1;
delete client[i].name;
delete client[i].data;
} else
process_cli(&client[i], recvbuf, n);
if (--nready <= 0) break; /* no more readable descriptors */
}
}
}
close(listenfd); /* close listenfd */
}
void process_cli(CLIENT *client, char* recvbuf, int len)
{
char sendbuf[MAXDATASIZE];
recvbuf[len-1] = '\0';
if (strlen(client->name) == 0) {
/* Got client's name from client */
memcpy(client->name,recvbuf, len);
printf("Client's name is %s.\n",client->name);
return;
}
/* save client's data */
printf("Received client( %s ) message: %s\n",client->name, recvbuf);
/* save user's data */
savedata(recvbuf,len, client->data);
/* reverse usr's data */
for (int i1 = 0; i1 < len - 1; i1++) {
sendbuf[i1] = recvbuf[len - i1 -2];
}
sendbuf[len - 1] = '\0';
send(client->fd,sendbuf,strlen(sendbuf),0);
}
void savedata(char* recvbuf, int len, char* data)
{
int start = strlen(data);
for (int i = 0; i < len; i++) {
data[start + i] = recvbuf[i];
}
}
// client.c
#include
#include
#include
#include
#include
#include
#include
#include
#define PORT 1234 /* Open Port on Remote Host */
#define MAXDATASIZE 100 /* Max number of bytes of data */
void process(FILE *fp, int sockfd);
char* getMessage(char* sendline,int len, FILE* fp);
int main(int argc, char *argv[])
{
int fd; /* files descriptors */
struct hostent *he; /* structure that will get information about remote host */
struct sockaddr_in server; /* server's address information */
if (argc !=2) {
printf("Usage: %s
exit(1);
}
if ((he=gethostbyname(argv[1]))==NULL){ /* calls gethostbyname() */
printf("gethostbyname() error\n");
exit(1);
}
if ((fd=socket(AF_INET, SOCK_STREAM, 0))==-1){ /* calls socket() */
printf("socket() error\n");
exit(1);
}
bzero(&server,sizeof(server));
server.sin_family = AF_INET;
server.sin_port = htons(PORT); /* htons() is needed again */
server.sin_addr = *((struct in_addr *)he->h_addr);
if(connect(fd, (struct sockaddr *)&server,sizeof(struct sockaddr))==-1){ /* calls connect() */
printf("connect() error\n");
exit(1);
}
process(stdin,fd);
close(fd); /* close fd */
}
void process(FILE *fp, int sockfd)
{
char sendline[MAXDATASIZE], recvline[MAXDATASIZE];
int numbytes;
printf("Connected to server. \n");
/* send name to server */
printf("Input name : ");
if ( fgets(sendline, MAXDATASIZE, fp) == NULL) {
printf("\nExit.\n");
return;
}
send(sockfd, sendline, strlen(sendline),0);
/* send message to server */
while (getMessage(sendline, MAXDATASIZE, fp) != NULL) {
send(sockfd, sendline, strlen(sendline),0);
if ((numbytes = recv(sockfd, recvline, MAXDATASIZE,0)) == 0) {
printf("Server terminated.\n");
return;
}
recvline[numbytes]='\0';
printf("Server Message: %s\n",recvline); /* it prints server's welcome message */
}
printf("\nExit.\n");
}
char* getMessage(char* sendline,int len, FILE* fp)
{
printf("Input string to server:");
return(fgets(sendline, MAXDATASIZE, fp));
}
