I/O多路复用中select指的是什么
时间：2023-05-14 00:34
select是用于监视多个文件描述符状态的变化的。即用来监视文件描述符读/写/异常状态是否就绪。 函数原型：int select(int nfds,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,struct timeval *timeout); select的几大缺点： （1）每次调用select，都需要把fd集合从用户态拷贝到内核态，这个开销在fd很多时会很大 （2）同时每次调用select都需要在内核遍历传递进来的所有fd，这个开销在fd很多时也很大 （3）select支持的文件描述符数量太小了 以上就是I/O多路复用中select指的是什么的详细内容，更多请关注Gxl网其它相关文章！ 1 #include<stdio.h> 2 #include<string.h> 3 #include<stdlib.h> 4 #include<unistd.h> 5 #include<sys/select.h> 6 7 int main() 8 { 9 int std_in = 0; 10 // int std_out = 1; 11 fd_set reads; 12 // fd_set writes; 13 //int max_nums = std_out; 14 int max_nums = std_in; 15 FD_ZERO(&reads); 16 // FD_ZERO(&writes); 17 FD_SET(std_in,&reads); 18 // FD_SET(std_out,&writes); 19 struct timeval _timeout = {5,0}; 20 int done = 0; 21 while(!done) 22 { 23 _timeout.tv_sec = 5; 24 _timeout.tv_usec = 0; 25 //switch(select(max_nums+1,&reads,&writes,NULL,&_timeout)) 26 switch(select(max_nums+1,&reads,NULL,NULL,&_timeout)) 27 { 28 case -1: 29 perror("select"); 30 break; 31 case 0: 32 printf("timeout...
"); 33 break; 34 default://success 35 { 36 if(FD_ISSET(std_in,&reads)) 37 {//read 38 char buf[1024]; 39 memset(buf,' ',sizeof(buf)); 40 ssize_t size = read(std_in,buf,sizeof(buf)-1); 41 if(size<0) 42 { 43 perror("read"); 44 exit(1); 45 } 46 if(strncmp(buf,"quit",4)==0) 47 { 48 done =1; 49 continue; 50 } 51 printf("echo: %s",buf); 52 53 } 54 // if(FD_ISSET(std_out,&writes)) 55 // {//writes 56 // char buf[1024]; 57 // while(1) 58 // { 59 // memset(buf,' ',sizeof(buf)); 60 // strcpy(buf,"hello world"); 61 //write(1,buf,sizeof(buf)-1); 62 // printf("%s
",buf); 63 // } 64 // } 65 break; 66 } 67 } 68 } 69 return 0; 70 } [fbl@localhost select]$ ./select helloecho: hellohiecho: hinihaoecho: nihaoahhauecho: ahhauquit[fbl@localhost select]$ 1 #include<stdio.h> 2 #include<string.h> 3 #include<stdlib.h> 4 #include<unistd.h> 5 #include<sys/socket.h> 6 #include<sys/select.h> 7 #include<sys/types.h> 8 #include<netinet/in.h> 9 #include<arpa/inet.h> 10 #include<assert.h> 11 12 #define _BACKLOG_ 5 13 int fd[64]; 14 void usage(char *_port) 15 { 16 printf("%s,[ip],[port]
",_port); 17 } 18 int startup(char *ip,int port) 19 { 20 assert(ip); 21 int sock = socket(AF_INET,SOCK_STREAM,0); 22 if(sock<0) 23 { 24 perror("socket"); 25 exit(1); 26 } 27 struct sockaddr_in local; 28 local.sin_family = AF_INET; 29 local.sin_port = htons(port); 30 local.sin_addr.s_addr = inet_addr(ip); 31 if(bind(sock,(struct sockaddr*)&local,sizeof(local))<0) 32 { 33 perror("bind"); 34 exit(2); 35 } 36 if(listen(sock,_BACKLOG_)<0) 37 { 38 perror("listen"); 39 exit(3); 40 } 41 return sock; 42 43 44 } 45 int main(int argc,char *argv[]) 46 { 47 if(argc!=3) 48 { 49 usage(argv[0]); 50 return 1; 51 } 52 int port = atoi(argv[2]); 53 char *ip = argv[1]; 54 int listen_sock = startup(ip,port); 55 int new_sock = -1; 56 struct sockaddr_in client; 57 socklen_t len = sizeof(client); 58 fd_set reads; 59 fd_set writes; 60 int max_nums; 61 struct timeval _timeout = {5,0}; 62 int done = 0; 63 int i =0; 64 int fd_nums = sizeof(fd)/sizeof(fd[0]); 65 for(;i<fd_nums;++i) 66 { 67 fd[i]=-1; 68 } 69 fd[0] = listen_sock; 70 while(!done) 71 { 72 _timeout.tv_sec = 5; 73 _timeout.tv_usec = 0; 74 FD_ZERO(&reads); 75 FD_ZERO(&writes); 76 for(i=0;i<fd_nums;++i) 77 { 78 if(fd[i]>0) 79 { 80 FD_SET(fd[i],&reads); 81 if(fd[i]>max_nums) 82 { 83 max_nums = fd[i]; 84 } 85 86 } 87 } 88 switch(select(max_nums+1,&reads,&writes,NULL,&_timeout)) 89 { 90 case -1: 91 perror("select"); 92 break; 93 case 0: 94 printf("timeout...
"); 95 break; 96 default: 97 { 98 99 for(i=0;i<fd_nums;++i)100 {101 if(fd[i]==listen_sock && FD_ISSET(fd[i],&reads))102 {103 new_sock = accept(listen_sock,(struct sockaddr*) &client,&len);104 if(new_sock<0)105 {106 perror("accept");107 continue;108 }109 for(i=0;i<fd_nums;++i)110 {111 if(fd[i]==-1)112 {113 fd[i]=new_sock;114 }115 }116 117 }118 else if(fd[i]>0 && FD_ISSET(fd[i],&reads))119 {120 char buf[1024];121 memset(buf,' ',sizeof(buf));122 ssize_t size = read(new_sock,buf,sizeof(buf)-1);123 if(size<0)124 {125 perror("read");126 exit(4);127 }128 else if(size==0)129 {130 printf("client close...
");131 close(fd[i]);132 fd[i]=-1;133 }134 else135 {136 buf[size]=' ';137 }138 printf("client:%s
",buf);139 }140 else141 {}142 }143 144 break;145 }146 147 }148 }149 return 0;150 }1 #include<stdio.h> 2 #include<string.h> 3 #include<stdlib.h> 4 #include<unistd.h> 5 #include<sys/socket.h> 6 #include<sys/select.h> 7 #include<sys/types.h> 8 #include<netinet/in.h> 9 #include<arpa/inet.h> 10 void usage(char *_port) 11 { 12 printf("%s,[ip],[port]
",_port); 13 } 14 int main(int argc,char *argv[]) 15 { 16 if(argc!=3) 17 { 18 usage(argv[0]); 19 return 1; 20 } 21 int port = atoi(argv[2]); 22 char *ip = argv[1]; 23 int sock = socket(AF_INET,SOCK_STREAM,0); 24 if(sock<0) 25 { 26 perror("socket"); 27 exit(1); 28 } 29 struct sockaddr_in remote; 30 remote.sin_family = AF_INET; 31 remote.sin_port = htons(port); 32 remote.sin_addr.s_addr = inet_addr(ip); 33 int ret = connect(sock,(struct sockaddr*)&remote,sizeof(remote)); 34 if(ret<0) 35 { 36 perror("connect"); 37 exit(1); 38 } 39 char buf[1024]; 40 while(1) 41 { 42 43 memset(buf,' ',sizeof(buf)); 44 printf("please say:"); 45 scanf("%s",buf); 46 ssize_t size = write(sock,buf,sizeof(buf)-1); 47 if(size<0) 48 { 49 perror("write"); 50 exit(2); 51 } 52 else if(size ==0) 53 {} 54 else 55 { 56 printf("client : %s
",buf); 57 } 58 } 59 return 0; 60 }[fbl@localhost select_socket]$ ./server 192.168.1.106 8080timeout...client:helloclient:hiclient:huowoclient close...client:read: Bad file descriptor[fbl@localhost select_socket]$ [fbl@localhost select_socket]$ ./client 192.168.1.106 8080please say:helloclient : helloplease say:hiclient : hiplease say:huowoclient : huowoplease say:^C[fbl@localhost select_socket]$
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