linux socket的select函数例子

转自:http://www.cnblogs.com/faraway/archive/2009/03/06/1404449.html

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 );
}

转载于:https://www.cnblogs.com/hnrainll/archive/2011/05/05/2038241.html