socket 中 fcntl(),select()的介绍

一、fcntl()函数有如下特性：

1）非阻塞I/O： 可将cmd 设为F_SETFL,将lock设为O_NONBLOCK

#include <sys/types.h>#include <sys/socket.h>#include <sys/wait.h>#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <sys/un.h>#include <sys/time.h>#include <sys/ioctl.h>#include <unistd.h>#include <netinet/in.h>#include <fcntl.h>#include <unistd.h>#define SERVPORT 3333#define BACKLOG 10#define MAX_CONNECTED_NO 10#define MAXDATASIZE 100int main(){struct sockaddr_in server_sockaddr,client_sockaddr;int sin_size,recvbytes,flags;int sockfd,client_fd;char buf[MAXDATASIZE];/*创建socket*/if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}printf("socket success!,sockfd=%d\n",sockfd);/*设置sockaddr结构*/server_sockaddr.sin_family=AF_INET;server_sockaddr.sin_port=htons(SERVPORT);server_sockaddr.sin_addr.s_addr=INADDR_ANY;bzero(&(server_sockaddr.sin_zero),8);/*将本地ip地址绑定端口号*/if(bind(sockfd,(struct sockaddr *)&server_sockaddr,sizeof(struct sockaddr))==-1){perror("bind");exit(1);}printf("bind success!\n");/*监听*/if(listen(sockfd,BACKLOG)==-1){perror("listen");exit(1);}printf("listening....\n");/*fcntl()函数，处理多路复用I/O*/if((flags=fcntl( sockfd, F_SETFL, 0))<0)perror("fcntl F_SETFL");flags |= O_NONBLOCK;if(fcntl( sockfd, F_SETFL,flags)<0)perror("fcntl");while(1){sin_size=sizeof(struct sockaddr_in);if((client_fd=accept(sockfd,(struct sockaddr*)&client_sockaddr,&sin_size))==-1){  //服务器接受客户端的请求，返回一个新的文件描述符perror("accept");exit(1);}if((recvbytes=recv(client_fd,buf,MAXDATASIZE,0))==-1){perror("recv");exit(1);}if(read(client_fd,buf,MAXDATASIZE)<0){perror("read");exit(1);}  printf("received a connection :%s",buf);

<span style="font-family: Arial, Helvetica, sans-serif;">   /*关闭连接*/</span>

 close(client_fd); exit(1); /*while*/}

结果：

[root@localhost net]# ./fcntl
socket success!,sockfd=3
bind success!
listening....
accept: Resource temporarily unavailable

2)信号驱动I/O：可将cmd设为F_SETFL,将lock设为O_ASYNC.

           flags |= O_ASYNC; 
  if(fcntl( sockfd, F_SETFL,flags)<0)   perror("fcntl"); 

结果：

[root@localhost net]# ./fcntl1
socket success!,sockfd = 3
bind success!
listening...


二、 select

#include <sys/types.h>#include <sys/socket.h>#include <sys/wait.h>#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <sys/un.h>#include <sys/time.h>#include <sys/ioctl.h>#include <unistd.h>#include <netinet/in.h>#define SERVPORT 3333#define BACKLOG 10#define MAX_CONNECTED_NO 10#define MAXDATASIZE 100int main(){struct sockaddr_in server_sockaddr,client_sockaddr;int sin_size,recvbytes;fd_set readfd;fd_set writefd;int sockfd,client_fd;char buf[MAXDATASIZE];/*创建socket*/if((sockfd = socket(AF_INET,SOCK_STREAM,0))==-1){perror("socket");exit(1);}printf("socket success!,sockfd=%d\n",sockfd);/*设置sockaddr结构*/server_sockaddr.sin_family=AF_INET;server_sockaddr.sin_port=htons(SERVPORT);server_sockaddr.sin_addr.s_addr=INADDR_ANY;bzero(&(server_sockaddr.sin_zero),8);/*将本地ip地址绑定端口号*/if(bind(sockfd,(struct sockaddr *)&server_sockaddr,sizeof(struct sockaddr))==-1){perror("bind");exit(1);}printf("bind success!\n");/*监听*/if(listen(sockfd,BACKLOG)==-1){perror("listen");exit(1);}printf("listening....\n");/*select*/FD_ZERO(&readfd);              // 将readfd 清空 FD_SET(sockfd,&readfd);         //将sockfd加入到readfd集合中while(1){sin_size=sizeof(struct sockaddr_in);if(select(MAX_CONNECTED_NO,&readfd,NULL,NULL,(struct timeval *)0)>0){  //第一个参数是0和sockfd的最大值加1，第二个参数是读集，第三、四个参数是写集                                                                                //和异常集if(FD_ISSET(sockfd,&readfd)>0){         // FD_ISSET 这个宏判断 sockfd 是否属于可读的文件描述符。从 sockfd 中读入, 输出到标准输出上去.if((client_fd=accept(sockfd,(struct sockaddr *)&client_sockaddr,&sin_size))==-1){   //client_sockaddr：客户端地址perror("accept");exit(1);}if((recvbytes=recv(client_fd,buf,MAXDATASIZE,0))==-1){perror("recv");exit(1);}if(read(client_fd,buf,MAXDATASIZE)<0){perror("read");exit(1);}printf("received a connection :%s",buf);}/*if*/close(client_fd);}/*select*/}/*while*/}

 结果 ：
[root@localhost net]#  gcc select1.c -o select1
[root@localhost net]# ./select1
socket create success!
bind success!
listening...