linux socket的select函数例子

使用select函数可以以非阻塞的方式和多个socket通信。程序只是演示select函数的使用,功能非常简单,即使某个连接关闭以后也不会修改当前连接数,连接数达到最大值后会终止程序。

1. 程序使用了一个数组fd_A,通信开始后把需要通信的多个socket描述符都放入此数组。

2. 首先生成一个叫sock_fd的socket描述符,用于监听端口。

3. 将sock_fd和数组fd_A中不为0的描述符放入select将检查的集合fdsr。

4. 处理fdsr中可以接收数据的连接。如果是sock_fd,表明有新连接加入,将新加入连接的socket描述符放置到fd_A。

#include <stdio.h>
#include
<stdlib.h>
#include
<unistd.h>
#include
<errno.h>
#include
<string.h>
#include
<sys/types.h>
#include
<sys/socket.h>
#include
<netinet/in.h>
#include
<arpa/inet.h>

#define MYPORT 1234 // the port users will be connecting to

#define BACKLOG 5 // how many pending connections queue will hold

#define BUF_SIZE 200

int fd_A[BACKLOG]; // accepted connection fd
int conn_amount; // current connection amount

void showclient()
{
int i;
printf(
"client amount: %d\n", conn_amount);
for (i = 0; i < BACKLOG; i++) {
printf(
"[%d]:%d ", i, fd_A[i]);
}
printf(
"\n\n");
}

int main(void)
{
int sock_fd, new_fd; // listen on sock_fd, new connection on new_fd
struct sockaddr_in server_addr; // server address information
struct sockaddr_in client_addr; // connector's address information
socklen_t sin_size;
int yes = 1;
char buf[BUF_SIZE];
int ret;
int i;

if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror(
"socket");
exit(
1);
}

if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
perror(
"setsockopt");
exit(
1);
}

server_addr.sin_family
= AF_INET; // host byte order
server_addr.sin_port = htons(MYPORT); // short, network byte order
server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
memset(server_addr.sin_zero, '\0', sizeof(server_addr.sin_zero));

if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
perror(
"bind");
exit(
1);
}

if (listen(sock_fd, BACKLOG) == -1) {
perror(
"listen");
exit(
1);
}

printf(
"listen port %d\n", MYPORT);

fd_set fdsr;
int maxsock;
struct timeval tv;

conn_amount
= 0;
sin_size
= sizeof(client_addr);
maxsock
= sock_fd;
while (1) {
// initialize file descriptor set
FD_ZERO(&fdsr);
FD_SET(sock_fd,
&fdsr);

// timeout setting
tv.tv_sec = 30;
tv.tv_usec
= 0;

// add active connection to fd set
for (i = 0; i < BACKLOG; i++) {
if (fd_A[i] != 0) {
FD_SET(fd_A[i],
&fdsr);
}
}

ret
= select(maxsock + 1, &fdsr, NULL, NULL, &tv);
if (ret < 0) {
perror(
"select");
break;
}
else if (ret == 0) {
printf(
"timeout\n");
continue;
}

// check every fd in the set
for (i = 0; i < conn_amount; i++) {
if (FD_ISSET(fd_A[i], &fdsr)) {
ret
= recv(fd_A[i], buf, sizeof(buf), 0);
if (ret <= 0) { // client close
printf("client[%d] close\n", i);
close(fd_A[i]);
FD_CLR(fd_A[i],
&fdsr);
fd_A[i]
= 0;
}
else { // receive data
if (ret < BUF_SIZE)
memset(
&buf[ret], '\0', 1);
printf(
"client[%d] send:%s\n", i, buf);
}
}
}

// check whether a new connection comes
if (FD_ISSET(sock_fd, &fdsr)) {
new_fd
= accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size);
if (new_fd <= 0) {
perror(
"accept");
continue;
}

// add to fd queue
if (conn_amount < BACKLOG) {
fd_A[conn_amount
++] = new_fd;
printf(
"new connection client[%d] %s:%d\n", conn_amount,
inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
if (new_fd > maxsock)
maxsock
= new_fd;
}
else {
printf(
"max connections arrive, exit\n");
send(new_fd,
"bye", 4, 0);
close(new_fd);
break;
}
}
showclient();
}

// close other connections
for (i = 0; i < BACKLOG; i++) {
if (fd_A[i] != 0) {
close(fd_A[i]);
}
}

exit(
0);
}

 

posted @ 2010-11-15 21:41  忧国忧铭  Views(16839)  Comments(0Edit  收藏  举报