Linux关于并发网络分为Apache模型（Process per Connection (进程连接) ） 和TPC ， 还有select模型，以及poll模型（一般是Epoll模型）
Select模型极其作用：这文章讲述的很好，没必要重述已有的东西，就直接给链接
http://blog.csdn.net/turkeyzhou/article/details/8609360
我的理解：
/* According to POSIX.1-2001 */
#include <sys/select.h> /* According to earlier standards */
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h> int select(int nfds, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, struct timeval *timeout); void FD_CLR(int fd, fd_set *set);
int FD_ISSET(int fd, fd_set *set);
void FD_SET(int fd, fd_set *set);
void FD_ZERO(fd_set *set);
对于
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
第一个参数 nfds： 第n个文件id的编号 （linux下，一切皆文件） 需要注意的是： nfds = fd+1 (fd 为 FD_SET中的fd)
第二个参数： fd_set *readfds 读取文件编号，如果不需要读取的话 可以设置为NULL
第三 ，四个参数： 同上
第五个参数：为一个定义超时的结构体
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
该结构用来设定多少时间为超时 ,比如
struct timeval ss ;
ss.tv_sec =;
ss.tv_usec =;
//表示设定为3秒后为超时，select将会返回0
对于下面这几个函数：
void FD_CLR(int fd, fd_set *set);
用来清除fd的fd_set ,比如fd为5 ，则表示set集中所有设定等于5的fd_set 都将被清除
int FD_ISSET(int fd, fd_set *set);
判断是否set 与fd是否绑定，如果没有绑定，则返回false，如果绑定了则返回True
void FD_SET(int fd, fd_set *set);
将fd值 和set绑定
void FD_ZERO(fd_set *set);
将set集全部清除
简单的例子：
判断是否有数据输入，有则直接打印出来
#include<stdio.h>
#include<string.h>
#include<sys/select.h>
#include<unistd.h>
#include<sys/time.h>
#include<sys/types.h>
#define maxn 6
#define EXIT_FAILURE -1
#define EXIT_SUCCESS 0 int main(int argc , char * argv []){ fd_set mtfd ;
int ffd =;
struct timeval outtime ;
int retval ;
char redbuf[maxn]; FD_ZERO(&mtfd);
FD_SET(ffd , &mtfd); // wait up to 5.5 s
outtime.tv_sec = ;
outtime.tv_usec = ;
retval = select(ffd+ , &mtfd ,NULL , NULL , &outtime);
if(- == retval )
{
printf("error happened ! %d \n" ,__LINE__ );
return EXIT_FAILURE ;
}
else if( == retval ){
printf(" timeout !! %d \n" ,__LINE__ );
return EXIT_FAILURE ;
}
//means that is good ! printf("retval = %d \n", retval); if( FD_ISSET(ffd , &mtfd) ){ memset(redbuf , , sizeof(redbuf));
printf("reading ... !! ");
// read(1 , redbuf ,sizeof(redbuf) ); //use the sys func
fread(redbuf , sizeof(redbuf) ,ffd+ , stdin );
}
// fwrite(redbuf ,strlen(redbuf) , 1 , stdout );
// write(1 , redbuf , strlen(redbuf));
printf("buf = %s buf_len = %d \n" , redbuf , strlen(redbuf)); return EXIT_SUCCESS ;
}
makefile文件：
.SUFFIXES: .o.c
CC =gcc
SRC = Se_keyboard.c
OBJ = $(SRC: .c =.o)
BIN = Se_keyboard .PHONY: start
start: $(OBJ)
$(CC) -o $(BIN) $(OBJ)
.o.c: $(SRC)
$(CC) -g -Wall $@ -c $<
.PHONY: clean
clean:
rm -f $(OBJ)
虽然知道这么多，但是还是觉得Select并没有什么作用。
Select一般是和Socket搭配使用，相当于线程池的效果，但是线程池有缺点，详情看这儿：
http://blog.csdn.net/tian*st/article/details/6677985
http://blog.csdn.net/xifeijian/article/details/17385831
关于Select的原理图：
首先来看下一对一的socket的c/s模式
关于socket的一对一的详解
http://www.cnblogs.com/gongxijun/p/4592864.html
看完这个之后，我们现在可以来看看这个图：
下面为举例：
服务器创建一个socket并bind绑定一个本机地址和设定一个端口，然后进入listen监听状态。采用select模型而非传统apache模型（ppc）或者tpc模型 。 不过Select模型就是有这样一个特点
一般我们default默认的SOMAXCONN为128 当然我们可以另外取一个设定（下面我们设定的是2048）作为最大连接数，虽然可以设置更大，但是缺点是，select模型是一个轮询模式，就是每一个都需要遍历一边所有的链接的fd
查看是否在fd_set集合中，这样，当SOMAXCONN取值非常大时，对于每一个客户端，访问时间都会延迟一点点，这样就是效率不是特别高！
下面是一个简单的多路复用的网络并发Select模型
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<netinet/in.h>
#include<netinet/ip.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<sys/time.h>
#include<arpa/inet.h>
#include<sys/select.h>
#include<assert.h> #ifndef EXIT_SUCCESS
#define EXIT_SUCCESS 0
#endif #ifndef EXIT_FAILURE
#define EXIT_FAILURE -1
#endif #define Max_connect 2048 //usually is SOMAXCONN =128 ,can be change #define maxn 1024
#define Port 5567
#define Ser_addr "192.168.132.128" #define ERROR_EXIT( inf ) \
do{ \
perror( inf ); \
printf("it happened in %d \n", __LINE__); \
exit(-); \
}while(); #define Waring( inf ) \
do{ \
perror( inf ); \
printf("it happened in %d \n", __LINE__); \
}while(); int fds[Max_connect];
int cnt = ; void
print (int fd, const char *str)
{
assert (str != NULL);
printf ("the fd is %d \n", fd);
puts (str);
} int
main (int argv, char *argc[])
{ int ser_sfd = -, i;
struct sockaddr_in ser_addr;
struct sockaddr_in client_addr;
int setfd = , optval, maxsockfd; char rebuf[maxn], wbuf[maxn]; // build a socket with ipv4 ans tcp if ((ser_sfd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP)) < )
ERROR_EXIT ("socket...!"); // set the type socket
/*
level ={ SOL_SOCKET ,IPPROTO_TCP}
setsockopt is to cancle the jiangsi process
*/ printf ("ser_sfd = %d \n", ser_sfd);
if (setsockopt (ser_sfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof (optval))
< )
ERROR_EXIT ("setsockopt...!"); memset (&client_addr, , sizeof (client_addr));
memset (&ser_addr, , sizeof (ser_addr));
ser_addr.sin_family = AF_INET;
ser_addr.sin_port = htons (Port);
ser_addr.sin_addr.s_addr = htonl (INADDR_ANY); if (bind (ser_sfd, (struct sockaddr *) &ser_addr, sizeof (ser_addr)) < )
ERROR_EXIT ("bind..!"); if (listen (ser_sfd, Max_connect) < )
ERROR_EXIT ("listen...!"); //user the select moduel
memset (fds, , sizeof (fds));
fd_set fdset, wfd;
maxsockfd = ser_sfd; //max socket fd struct timeval tout; tout.tv_sec = ;
tout.tv_usec = ; while ()
{ FD_ZERO (&fdset); //clear
//FD_ZERO (&wfd); FD_SET (ser_sfd, &fdset); //bind
//FD_SET (ser_sfd, &wfd); struct timeval tout; tout.tv_sec = ;
tout.tv_usec = ; for (i = ; i < cnt; i++)
{
if (fds[i] != )
FD_SET (fds[i], &fdset);
} int tag = select (maxsockfd + , &fdset, NULL, NULL, &tout); if (tag == )
{
Waring ("select wait timeout !");
continue;
}
else if (tag == -)
ERROR_EXIT ("Error select ...!"); //lunxun select
for (i = ; i < cnt; i++)
{ if (FD_ISSET (fds[i], &fdset))
{ int len = recv (fds[i], rebuf, sizeof (rebuf), );
if (len <= )
{ printf ("%d: \n", fds[i]);
close (fds[i]);
FD_CLR (fds[i], &fdset);
Waring ("client is closed !");
continue;
} printf ("the client_ip : %s\n",
inet_ntoa (client_addr.sin_addr)); print (fds[i], rebuf); send (fds[i], rebuf, sizeof (rebuf), ); //hui she
memset (rebuf, , sizeof (rebuf));
}
}
//if have a new connect happened
// memset(&client_addr , 0 ,sizeof(client_addr));
if (FD_ISSET (ser_sfd, &fdset))
{
// memset(&client_addr , 0 ,sizeof(client_addr));
int acplen = sizeof (client_addr);
int acp = accept (ser_sfd, (struct sockaddr *) &client_addr,
&acplen); printf ("accept return acp=%d \n", acp); if (acp < )
{ Waring ("waring accept acp<=0!");
continue;
}
//add to arr
if (cnt < maxn)
fds[cnt++] = acp;
else
{
ERROR_EXIT ("cnt>maxn");
}
if (acp > maxsockfd)
maxsockfd = acp;
}
} for (i = ; i < cnt; i++)
{
close (fds[i]);
} return EXIT_SUCCESS;
}
makefile文件：
.SUFFIXES: .o.c
CC =gcc
SRC = server.c
OBJ = $(SRC: .c =.o)
BIN = Sez_Server .PHONY: start
start: $(OBJ)
$(CC) -o $(BIN) $(OBJ)
.o.c: $(SRC)
$(CC) -g -Wall $@ -c $<
.PHONY: clean
clean:
rm -f $(OBJ)
客户端：
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<assert.h>
#include<unistd.h>
#ifndef EXIT_FAILURE
#define EXIT_FAILURE - //exit failure
#endif
#ifndef EXIT_SUCCESS
#define EXIT_SUCCESS // exit sucessful
#endif #define Port
#define IPADDR "192.168.132.128"
#define maxn #define ERROR_EXIT( inf ) \
do{ \
perror( inf ); \
printf("it's happened in %d \n",__LINE__); \
}while() ; //use the function to connect the server !! int
main (int argv, char *argc[])
{ int sfd = -;
char rbuf[maxn], wbuf[maxn];
// int sfd=- ; //socket_fd
int confd = -; //connect_fd
struct sockaddr_in soaddr;
if ((sfd = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP)) < )
{
ERROR_EXIT ("socket");
return EXIT_FAILURE;
} //memset a struct
memset (&soaddr, , sizeof (soaddr)); //int the struct sockaddr_in soaddr.sin_family = AF_INET;
soaddr.sin_port = htons (Port);
soaddr.sin_addr.s_addr = inet_addr (IPADDR); if ((confd =
connect (sfd, (struct sockadrr *) &soaddr, sizeof (soaddr))) < )
{
ERROR_EXIT ("connect");
return EXIT_FAILURE;
} printf ("connect is sucessful !\n"); while (fgets (wbuf, sizeof (rbuf), stdin) != NULL)
{
write (sfd, wbuf, strlen (wbuf));
read (sfd, rbuf, sizeof (rbuf));
fputs (rbuf, stdout);
} close (sfd);
close (confd);
return EXIT_SUCCESS;
}
makefile文件：
-
.SUFFIXES: .o.c
CC =gcc
SRC = client.c
OBJ = $(SRC: .c =.o)
BIN = Se_client .PHONY: start
start: $(OBJ)
$(CC) -o $(BIN) $(OBJ)
.o.c: $(SRC)
$(CC) -g -Wall $@ -c $<
.PHONY: clean
clean:
rm -f $(OBJ)效果图：
-