select是一個系統調用和應用程序編程接口(API)在類Unix和POSIX兼容的操作系統用於檢查的狀態文件描述符打開輸入/輸出通道。選擇系統調用是類似的調查在UNIX System V和更高版本的操作系統推出設施.
函數如下:
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout);
fd_set type參數可以具有四個工具宏來處理:FD_SET(),FD_CLR(),FD_ZERO() ,和FD_ISSET() 。(這裏便不細說了,有疑問的讀者可以man)
選擇回報位設置總數readfds,writefds和errorfds,或零如果超時到期,-1。
文件描述符在選擇所使用的集合是有限的大小,取決於操作系統。較新的系統調用輪詢提供了更靈活的解決方案。
select服務器代碼如下
<span style="font-size:18px;">#include<stdio.h>
#include<sys/socket.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<unistd.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<stdlib.h>
#include<sys/time.h>
char fds[128];
#define COUNT sizeof(fds)/sizeof(fds[0])
int max_fd = 0;
static void guse(const char* prac)
{
printf("%s [ip] [port]..\n",prac);
}
static int my_select(const char* _ip, const int _port){
int sock = socket(AF_INET,SOCK_STREAM,0);
if(sock < 0){
perror("create socket error...");
exit(1);
}
struct sockaddr_in server_socket;
bzero(&server_socket,sizeof(server_socket));
server_socket.sin_family = AF_INET;
server_socket.sin_addr.s_addr =inet_addr(_ip);
server_socket.sin_port = htons(_port);
int opt = 1;
setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));
if(bind(sock,(struct sockaddr*)&server_socket,sizeof(server_socket))< 0)
{
perror("bind error ...");
exit(2);
}
if(listen(sock,5) < 0 ){
perror("listen errno ...");
close(sock);
exit(3);
}
return sock;
}
static void init_fd_arr()
{
int i = 0;
for(;i<COUNT;i++){
fds[i] = -1;
}
}
static int add_fd_arr(int fd){
int i = 0;
for(;i<COUNT;i++){
if(fds[i] == -1){
fds[i] = fd;
return 0;
}
}
return i;
}
static int remove_arr(int fd){
int i = 0;
for(; i < COUNT; i++){
if(fds[i] == fd){
fds[i] = -1;
break;
}
}
return 0;
}
static int setifd(fd_set * fdset){
int i = 0;
for(;i<COUNT;i++){
if(fds[i] != -1 ){
FD_SET(fds[i],fdset);
if(fds[i]>max_fd)
max_fd = fds[i];
}
}
return 0;
}
int main(int argc,char* argv[])
{
if(argc != 3)
{
guse(argv[0]);
exit(0);
}
init_fd_arr();
int listen_sock = my_select(argv[1], atoi(argv[2]));
add_fd_arr(listen_sock);
fd_set red;
FD_ZERO(&red);
while(1){
setifd(&red);
FD_SET(listen_sock,&red);
struct timeval _timeout ={5,0};
switch(select(max_fd+1,&red,NULL,NULL,&_timeout)){
case -1:
printf("selsect errno..\n");
exit(4);
break;
case 0:
printf("Time out \n");
break;
default:
{
int index = 0;
for(;index < COUNT; index++){
if(fds[index] != -1 && FD_ISSET(fds[index],&red)){
struct sockaddr_in peer;
int addrlen = sizeof(peer);
int ret = accept(listen_sock,(struct sockaddr*)&peer,&addrlen);
if(ret < 0){
perror("accept error...\n");
close(ret);
exit(4);
}else
{
if(1 == add_fd_arr(ret)){
printf("full ...\n");
close(ret);
}
}
printf("Yougot a connection from cient's ip is %s, prot is %d\n",inet_ntoa(peer.sin_addr),htons(peer.sin_port));
continue;
}
}
if(fds[index] != -1 && FD_ISSET(fds[index],&red)){
char buf[1024];
memset(buf,'\0',sizeof(buf));
ssize_t _s = read(fds[index],buf,sizeof(buf)-1);
if(_s == 0){
printf("client close ...\n");
}
else if(_s < 0)
{
printf("errno read..\n");
}
else{
printf("server:%s",buf);
}
}
}
break;
}
}
return 0;
}
</span>
首先我們來看看這個這個程序的結果:
可以看出,這個程序跟上一篇TCP服務器的功能是一樣的。至於客戶端,讀者可以去看上一篇博文,這篇文章便不再敘說。
poll:
<span style="font-size:18px;">#include<stdio.h>
#include<poll.h>
#include<errno.h>
#include<string.h>
#include<stdlib.h>
int main()
{
struct pollfd polls[1];
polls[0].fd = 0;
polls[0].events = POLLIN;
polls[0].revents = 1;
int times = 5000;
char buf[1024];
while(1)
{
switch(poll(polls,1,times)){
case -1:
printf("poll error...\n");
exit(0);
break;
case 0:
printf("Time OUT ...\n");
break;
default:
{
memset(buf,'\0',sizeof(buf));
read(1,buf,sizeof(buf));
printf("%s\n",buf);
}
break;
}
}
return 0;
}
</span>
這個程序的功能是你輸入一個字符,然後服務器給你返回那個值: