使用select函数能够以非堵塞的方式和多个socket通信。程序仅仅是演示select函数的使用，功能很easy，即使某个连接关闭以后也不会改动当前连接数。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，通信開始后把须要通信的多个socket描写叙述符都放入此数组。
2. 首先生成一个叫sock_fd的socket描写叙述符，用于监听port。
3. 将sock_fd和数组fd_A中不为0的描写叙述符放入select将检查的集合fdsr。
4. 处理fdsr中能够接收数据的连接。假设是sock_fd，表明有新连接增加。将新增加连接的socket描写叙述符放置到fd_A。
这部分代码实现逻辑不错，只是有点bug，对套接字缓存未做处理完整。
#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
", conn_amount);
for (i = 0; i < BACKLOG; i++) {
printf("[%d]:%d ", i, fd_A[i]);
}
printf("
");
}
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, ' ', 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
", 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
");
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
", 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], ' ', 1);
printf("client[%d] send:%s
", 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
", 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
");
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);
}
for(i=0;i<BACKLOG;i++)
{
tcpSockIndex[i] = -1;
}
while(1)
{
FD_ZERO(&readfds);
FD_SET(tcpSock, &readfds);
maxfdp = maxfdp>tcpSock?maxfdp:tcpSock;
for(i=0;i<BACKLOG;i++)
{
// AB_LOG("FD_SET tcpSockIndex[%d] = %d.
", i, tcpSockIndex[i]);
if(-1 != tcpSockIndex[i])
{
FD_SET(tcpSockIndex[i], &readfds);
maxfdp = maxfdp>tcpSockIndex[i]?maxfdp:tcpSockIndex[i];
}
}
timeout.tv_sec = SELECT_TIME_OUT_TM;
timeout.tv_usec = 0;
ret = select(maxfdp+1, &readfds, NULL, NULL, &timeout);
if(ret < 0)
{
AB_PERROR("select error!
");
return ;
}
else if(0 == ret)
{
AB_PERROR("select time out!
");
}
//处理client发送的报文
for(i=0; i<BACKLOG; i++)
{
if ( -1 != tcpSockIndex[i] &&
FD_ISSET(tcpSockIndex[i], &readfds))
{
AB_LOG("--- tcp client ---.
");
pthread_t pthd2;
TCP_SOCK_T * pTcpSock = NULL;
pTcpSock = (TCP_SOCK_T *)malloc(sizeof(TCP_SOCK_T));
pTcpSock->sock = tcpSockIndex[i];
pthread_create(&pthd2, NULL, bc_sock_handle_client_data, (void *)pTcpSock);
#if 0
bc_sock_handle_client_data(tcpSockIndex[i]);
ret = read(tcpSockIndex[i], NULL, 0);
AB_LOG("close tcpSockIndex[%d] = %d, ret = %d.
", i, tcpSockIndex[i], ret );
//关闭client连接的套接字
if(-1 == tcpSockIndex[i]) close(tcpSockIndex[i]);
#endif
//清空client字符集
FD_CLR(tcpSockIndex[i], &readfds);
tcpSockIndex[i] = -1;
tcpClientConnNum --;
}
}
//获取client连接过来的套接字
if(FD_ISSET(tcpSock, &readfds))
{
AB_LOG("--- tcp server ---.
");
if((tcpSockClient = accept(tcpSock,
(struct sockaddr*)&chiAddr, &cliLen)) <= 0 )
{
AB_PERROR("BCHV accept socket error: %s(errno: %d).
",strerror(errno), errno);
continue;
}
//在套接字数组中找出一个可用加入的位置。
for(i=0,tcpSockFlag=0; i<BACKLOG; i++)
{
AB_LOG("tcpSockIndex[%d] = %d.
", i, tcpSockIndex[i]);
if(-1 == tcpSockIndex[i])
{
tcpSockIndex[i] = tcpSockClient;
tcpClientConnNum ++;
AB_LOG("new connection client[%d] %08X:%d.
", tcpClientConnNum,
chiAddr.sin_addr.s_addr, ntohs(chiAddr.sin_port));
//错误打印
//AB_LOG("new connection client[%d] %s.
", tcpClientConnNum,
// inet_ntoa(chiAddr.sin_addr));
#if 0
if (sock_c > maxfdp)
maxfdp = sock_c;
#endif
tcpSockFlag = 1;
break;
}
}
//超过最大连接请求。能够发送client断开连接
if(0 == tcpSockFlag)
{
AB_LOG("max connections arrive, exit
");
send(tcpSockClient, "bye", 4, 0);
close(tcpSockClient);
}
}
}
//关闭全部client套接字
for(i=0; i<BACKLOG; i++)
{
if(-1 != tcpSockIndex[i])
{
close(tcpSockIndex[i]);
}
}
文章摘自 http://www.cnblogs.com/faraway/archive/2009/03/06/1404449.html