select--of I/O multiplexing based on TCP protocol

1. Basic knowledge about Select

   A. Select is a system-supplied multiplexed input-output model. It is used to monitor the state changes of multiple file handles.

   B. The program will stop at select and so on until at least one of the monitored file handles has changed state.

   C. File handle is an integer

   
   

2. Function

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A. Parameters

Nfds: The maximum file descriptor value to be monitored plus 1;

The struct TIMEVAL structure is used to describe a length of time, and if this time is exceeded, the descriptor that needs to be monitored does not occur and returns 0.

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3. Code implementation

 21     // 22     int sock=socket (AF_INET, sock_stream,0);  23     if (sock<0)  24     {  25         perror ("socket"); 26          exit (1); 27     } 28      // 28          // 29      struct sockaddr_in local; 30     local.sin_family=AF_INET;  31     local.sin_port=htons (port); 32      LOCAL.SIN_ADDR.S_ADDR=INET_ADDR (IP); 33     // 34      if (Bind (sock, (struct sockaddr*) &local,sizeof (local)) <0)  35      { 36          perror ("Bind"); 37          Exit (2); 38     } 39     // 40      if (Listen (Sock,_backlog_) <0)  41     { 42          perror ("Listen"); 43          exit (3); 44     } 45     return  Sock; 46 } 47 int main (int argc,char*argv[])  48 { 49      if (argc!=3)  50     { 51          usage (Argv[0]);  52         exit (1);  53     } 54  55     char* ip=argv[ 1]; 56  &nBsp;  int port=atoi (argv[2]); 57  58     int  Listen_sock=startup (ip,port);  59  60     int done=0; 61      int new_sock=-1; 62     struct sockaddr_ in client; 63     socklen_t len=sizeof (client);  64  65      int max_fd; 66     fd_set _reads;  67     fd_set _writes; 68  69     int  i=0; 70     int fds_num=sizeof (FDS)/sizeof (fds[0]); 71      for (; i<fds_num;++i)  72     { 73          fds[i]=-1; 74     } 75      fds[0]=listen_sock; 76     max_fd=fds[0]; 77  78      while (!done)  79     { 80          fd_zero (&_reads);  81         fd_zero (&_writes) ;  82         fd_set (listen_sock,&_reads); 83          struct timeval _timeout={5,0}; 84          for (i=1;i<fds_num;++i)  85          { 86              if (fds[i]>0)  87             {  88                  Fd_set (fds[i],&_reads); &nbSp;89                 if ( FDS[I]&GT;MAX_FD)  90                  { 91                      max_fd=fds[i]; 92                  } 93              } 94          } 95         switch (SELECT (max_fd+1,&_reads,&_ Writes,null,null))  96         { 97              case 0: 98                  //timeout 99                  printf ("timeout\n");100                  break;101              case -1:102                  perror ("select");103                  break;104              default:105                  {106                      i=0;107                       for (; i<fds_num;++i) 108                       {109                          if (Fds[i]==listen_sock&&fd_isset (fds[i],&_ reads)) 110                          {111                               //listen socket is ready!112                               new_sock=accePT (Listen_sock, (struct sockaddr*) &client,&len);113                               if (new_sock<0) 114                              { 115                                  perror ("Accept ");116                                  continue;117                               }118                               printf ("get a new connect...%d\n", New_sock);119                               for (i=0;i<fds_num;++i) 120                               {121                                  if (fds[i ]==-1) 122                                  {123                                       fds[i]=new_sock;124                                       break; 125                                  }126                               }127             &nBsp;                if (I==fds_ NUM) 128                              {129                                   close (New_sock);130                               }131                          }132                           //listen socket133                          else if (fds[i]>0 && fd_ ISSET (fds[i],&_reads)) 134                          {135                               char buf[1024];136                               ssize_t _s=read (fds[i],buf,sizeof (BUF)-1);137                               if (_s>0) 138                              {139                                   //read sucess140                                   buf[_s]= ';141                                   printf ("client:%s\n", buf);142                               }143                              else if (_s==0) 144                              {145                                   //client shutdown146                                   printf ("client shutdown...\n"); 147                         &nbsP;         close (Fds[i]);148                                   fds[i]=-1;149                               }150                              else151                               {152                                    perror ("read");153                              }154                           }155                          //normal  socket156                          else157                          {}158                       }159                 }160                  break;161          }162     }163      return 0;164 }

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select--of I/O multiplexing based on TCP protocol