IO multiplexing and signal driving, io Multiplexing Signal

IO multiplexing and signal driving, io Multiplexing Signal

Linux provides many interfaces for Multiplexing I/O, including select (), pselect (), and poll (). These interfaces are inherited from the BSD and System V factions.

The select model is relatively simple. "Round Robin" checks the status of fd_set and then takes corresponding measures.

It is necessary to take a closer look at the signal-driven model. The steps are as follows:

The following describes the client routine.

I wrote a demo of the chat program and used both technologies. The server uses the multiplexing I/O method instead of the Multi-Inbound (line) model. The customer service uses a signal drive, as shown below:

Comments are written to all places that are prone to bugs.

Serv. c

  1 #include <sys/select.h>  2 #include <sys/socket.h>  3 #include <netinet/in.h>  4 #include <arpa/inet.h>  5 #include <unistd.h>  6 #include <fcntl.h>  7 #include <stdlib.h>  8 #include <string.h>  9 #include <stdio.h> 10 #include <signal.h> 11  12 void endServ(int sig) 13 { 14     printf("Server ended!\n"); 15     exit(-1); 16 } 17  18 int main() 19 { 20     // signal 21     struct sigaction act; 22     sigemptyset(&act.sa_mask); 23     act.sa_handler = endServ; 24     act.sa_flags = 0; 25     sigaction(SIGINT,&act,0); 26     printf("This server is started,enter CTRL+C to end. \n"); 27  28     int servfd = socket(AF_INET,SOCK_STREAM,0); 29     if(servfd == -1) { 30         printf("something wrong with socket():%m\n"); 31         exit(-1); 32     } 33  34     struct sockaddr_in addr; 35     addr.sin_family = AF_INET; 36     addr.sin_port = htons(9999); 37     inet_pton(AF_INET,"127.0.0.1",&addr.sin_addr); 38  39     if (bind(servfd,(struct sockaddr*)&addr,sizeof(addr)) == -1) { 40         printf("Some thing wrong with bind():%m\n"); 41         exit(-1); 42     } 43     printf("Bind success!\n"); 44  45     listen(servfd,20); 46      47     int numbers=0;//how many clients has accepted 48     fd_set fs; 49     FD_ZERO(&fs); 50     int client_fd[100]; 51     int i; 52     for(i=0;i<100;++i) 53     { 54         client_fd[i] = -1; 55     } 56  57     int maxfd=0; 58     char buf[1024]; 59     for(;;) 60     { 61         maxfd =0; 62         FD_ZERO(&fs); 63         FD_SET(servfd,&fs); 64         maxfd = maxfd>servfd?maxfd:servfd; 65         for(i=0;i<numbers;++i) 66         { 67             if(client_fd[i] != -1) { 68                 FD_SET(client_fd[i],&fs); 69                 maxfd = maxfd>client_fd[i]?maxfd:client_fd[i]; 70             } 71         } 72  73         int res = select(maxfd+1,&fs,0,0,0); 74         if(res == -1) { 75             printf("Something wrong with select():%m\n"); 76             exit(-1); 77         } 78  79         if(FD_ISSET(servfd,&fs) && numbers < 100) { 80             printf("New client!\n"); 81             client_fd[numbers] = accept(servfd,0,0); 82             numbers++; 83         } 84          85         for(i=0;i<numbers;++i) 86         { 87             bzero(buf,sizeof(buf)); 88             //judge if client_fd[i] equal -1 is necessary 89             //if a client quited,next time the program will 90             //have a segment default 91             //also it should be in the front. 92             if(client_fd[i] != -1 && FD_ISSET(client_fd[i],&fs))  93             { 94                 res = recv(client_fd[i],buf,sizeof(buf),0); 95                 if(res == 0) { 96                     printf("A client quit\n"); 97                     close(client_fd[i]); 98                     FD_CLR(client_fd[i],&fs); 99                     client_fd[i] = -1;100                 }101                 else if(res == -1) {102                     printf("Something wrong with net.\n");103                     exit(-1);104                 }105                 else {106                     int j;107                     for(j=0;j<numbers;++j)108                     {109                         if(client_fd[j] != -1)110                             send(client_fd[j],buf,sizeof(buf),0);111                     }112                 }113             }114         }115     }116 }

 

Client:

 1 #include <signal.h> 2 #include <unistd.h> 3 #include <sys/socket.h> 4 #include <fcntl.h> 5 #include <arpa/inet.h> 6 #include <netinet/in.h> 7 #include <stdio.h> 8 #include <string.h> 9 #include <stdlib.h>10 #include <errno.h>11 12 static int fd;13 14 void show(int sig)15 {16     char buf[1024] = {0};17     int n = read(fd,buf,sizeof(buf));18     buf[n] = 0;19     write(1,"MSG:",strlen("MSG:"));20     write(1,buf,strlen(buf));21 }22 23 int main()24 {25     struct sigaction act;26     sigemptyset(&act.sa_mask);27     act.sa_handler = show;28     //This is necessary,in last loop read() counld be interrupt;29     act.sa_flags = SA_RESTART;30     sigaction(SIGIO,&act,0);31 32     fd = socket(AF_INET,SOCK_STREAM,0);33     if(fd == -1) {34         printf("Cannot get socketfd!:%m\n");35         exit(-1);36     }37 38     struct sockaddr_in addr;39     addr.sin_family = AF_INET;40     addr.sin_port = htons(9999);41     inet_pton(AF_INET,"127.0.0.1",&addr.sin_addr);42 43     if(connect(fd,(struct sockaddr*)&addr,sizeof(addr)) != -1)44         printf("connect success!\n");45     else46         exit(-1);47 48     int flag = fcntl(fd,F_GETFL);49     flag |= O_ASYNC;50     fcntl(fd,F_SETFL,flag);51     fcntl(fd,F_SETOWN,getpid());52 53     char buffer[1024]={0};54     for(;;)55     {56         int n = read(0,buffer,sizeof(buffer));57         if(n==-1)58             break;59         send(fd,buffer,n,0);60     }61 62     write(1,"Closed.",strlen("Closed."));63 }