function poll() trouble

harvest · 10-08-2006, 02:05 PM

Code:


/*
* serv.c - server creating AF_UNIX socket used by cli.c
* compile with gcc -g -Wall serv.c -o serv
* command line option: max number of clients allowed
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/poll.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>

#define UN_PATH "./usock"

static void add_flags ( int fd, int flags ) {
  int val;

  if (( val = fcntl ( fd, F_GETFL, 0 )) < 0 ) {
    perror ("add_flags (): fcntl ( F_GETFL )");
    exit(1);
  }
  val |= flags;
  if (( val = fcntl ( fd, F_SETFL, val )) < 0 ) {
    perror ("add_flags (): fcntl ( F_SETFL )");
    exit (1);
  }
}

int main ( int argc, char *argv[] ) {
  struct sockaddr_un  sa;
  struct pollfd      *pfd;
  socklen_t           cli_len;
  int                 srv, len, cli, cli_num, cli_now, n, l;
  char                buf[256];

  ( void )unlink ( UN_PATH );

  if (( argc != 2 ) || (( cli_num = atoi ( argv[1])) == 0 )) cli_num = 1;
  printf ( "Up to %d client(s) allowed\n", cli_num );
  
  cli_num++;   // one more for listen
  if (( pfd = ( pollfd * )calloc ( cli_num, sizeof ( pollfd ))) == NULL ) {
    perror ("calloc ( pollfd )");
    exit (1);
  }

  srv = socket ( PF_UNIX, SOCK_STREAM, 0 );
  if ( srv < 0 ) {
    perror ("socket ( PF_UNIX, SOCK_STREAM )");
    exit (1);
  }
  if ( fcntl ( srv, F_SETOWN, getpid ()) < 0 ) {
    perror ("fcntl ( s, F_SETOWN )");
    exit (1);
  }

  len = sizeof ( sa );
  sa.sun_family = AF_UNIX;
  strcpy ( sa.sun_path, UN_PATH );
  if ( bind ( srv, ( struct sockaddr * )&sa, len ) < 0 ) {
    perror ("bind ()");
    exit (1);
  }
  fprintf ( stderr, "bind () OK\n");

  if ( listen ( srv, 2 * cli_num + 3 ) < 0 ) {
    perror("listen ()");
    exit (1);
  }
  fprintf ( stderr, "listen () OK\n");

  pfd[0].fd = srv;
  pfd[0].events = POLLRDNORM;
  cli_now = 0;
  
  fprintf ( stderr, "Initializing loop:");
  for ( int i = 1; i < cli_num; i++ ) { 
    fprintf ( stderr, "." );
    pfd[i].fd = -1;
  }  
  fprintf ( stderr, "\nEntering loop\n");
  for ( ;; ) {
    n = poll ( pfd, cli_now + 1, -1 ); // no tmo
    fprintf ( stderr, "Aha!\n");
    if ( pfd[0].revents & POLLRDNORM ) { // new client
		  if ( cli_now < cli_num ) {
        if (( cli = accept ( srv, NULL, NULL )) < 0 ) perror ("accept()");
  		  else {
  		    fprintf ( stderr, "accept() OK\n: " );
          for ( int i = 1; i < cli_num; i++ ) { 
            if ( pfd[i].fd == -1 ) { 
              pfd[i].fd = cli;
              pfd[i].events = POLLRDNORM;
              cli_now++;
              fprintf ( stderr, "client#%d\n", cli_now );
              break;
            }
          }
        }
      }
      else fprintf ( stderr, "Too many clients\n" );
      if ( n == 1 ) continue;
    }
    for ( int i = 1; i < cli_num; i++ ) { 
//fprintf ( stderr, "." );
      if (( cli = pfd[i].fd ) < 0 ) continue;   
//      fprintf ( stderr, "pfd[%d].revents=%X\n", i, pfd[i].revents );
      if ( pfd[i].revents & ( POLLRDNORM | POLLERR )) {
        l = read ( cli, buf, sizeof ( buf ));
        if ( l < 0 ) {
          if ( errno == ECONNRESET ) {   // connection reset by client
            close ( cli );
            pfd[i].fd = -1;    
            cli_now--;
            fprintf ( stderr, "connection reset by client\n" );
          }
          else perror ("read()");
        }
        else if ( l == 0 ) {
          close ( cli );
          pfd[i].fd = -1;    
          cli_now--;
          fprintf ( stderr, "connection closed by client\n" );
        }
        else {
          buf[l++] = '\n';
          buf[l] = 0;
          fprintf ( stderr, "%s", buf );
        }
        if ( --n <= 0 ) break;
      }
    }
  }
/* not reached */
  return 0;
}

/*************************/
/*
* cli.c - client creating AF_UNIX socket
* compile with gcc -g -Wall cli.c -o cli
* command line option: client name
*/


#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define USOCK "./usock"

int main ( int argc, char *argv[]) {
  int    fd, len;
  FILE   *file;
  struct sockaddr_un sa;
  
  char buf1[50] = "hello from client ";
  int len1 = strlen ( buf1 );

  if( argc > 1 ){
    strcpy ( buf1 + len1, argv[1]);
    len1 = strlen(buf1);
  }
  
  fd = socket ( PF_UNIX, SOCK_STREAM, 0 );
  if ( fd < 0 ) {
    perror ("cli: socket ( PF_UNIX,SOCK_STREAM)");
    exit (1);
  }
  file = fdopen(fd, "wb+");
  if ( file == NULL ) {
    printf ("FILE fdopen failed\n");  
    exit (1);
  }
  sa.sun_family = AF_UNIX;
  strcpy ( sa.sun_path, USOCK );
  len = sizeof ( sa );
  if ( connect ( fd, ( struct sockaddr *)&sa, len ) < 0 ) {
    perror ("cli: connect()");
    exit (1);
  }
  
  for ( ;; ) {
    static unsigned long int count = 1;
    sleep ( 1 );
    printf ("Sent message #%d\n", count++ );
    if ( write ( fd, buf1, len1 ) != len1 ) {
      perror("cli: send(buf1)");
      exit(1);
    }
    fflush ( file );
  }
  return 0;
}

Start server with the option 2: ./serv 2
Start client with the option A: ./cli A
Server now is getting messages from client A
Start client with the option B: ./cli B
Server now is getting messages from both clients A and B

Terminate client B ( press ctrl+C )
Server now is getting messages from client A
Start client with the option B: ./cli B
Server now is getting messages from both clients A and B

Terminate client A ( press ctrl+C )
NOTHING IS COMING TO THE SCREEN!!!

Start client with the option A: ./cli A
Server now is getting messages from both clients A and B and from the client B you can get everything send while client A was off. My investigation showed that server was stock in the function call poll().
What do I do wrong or what I didn't get from the description of poll()
Thanks.

harvest · 10-08-2006, 03:42 PM

Below is updated code. It does what it should do. The question remains: why the original code does NOT work. The function poll() description does NOT require to do what makes it work. I'm totally confused.
Hey, NIX Guru, I want to hear from you!

Code:

                                                              /*
* serv.c - server creating AF_UNIX socket used by cli.c
* compile with gcc -g -Wall serv.c -o serv
*/

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/poll.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>

#define UN_PATH "./usock"

static void add_flags ( int fd, int flags ) {
  int val;

  if (( val = fcntl ( fd, F_GETFL, 0 )) < 0 ) {
    perror ("add_flags (): fcntl ( F_GETFL )");
    exit(1);
  }
  val |= flags;
  if (( val = fcntl ( fd, F_SETFL, val )) < 0 ) {
    perror ("add_flags (): fcntl ( F_SETFL )");
    exit (1);
  }
}

int main ( int argc, char *argv[] ) {
  struct sockaddr_un  sa;
  struct pollfd      *pfd;
  socklen_t           cli_len;
  int                 srv, len, cli, cli_num, cli_now, n, l;
  char                buf[256];

  ( void )unlink ( UN_PATH );

  if (( argc != 2 ) || (( cli_num = atoi ( argv[1])) == 0 )) cli_num = 1;
  printf ( "Up to %d client(s) allowed\n", cli_num );
  
  cli_num++;   // one more for listen
  if (( pfd = ( pollfd * )calloc ( cli_num, sizeof ( pollfd ))) == NULL ) {
    perror ("calloc ( pollfd )");
    exit (1);
  }

  srv = socket ( PF_UNIX, SOCK_STREAM, 0 );
  if ( srv < 0 ) {
    perror ("socket ( PF_UNIX, SOCK_STREAM )");
    exit (1);
  }
  if ( fcntl ( srv, F_SETOWN, getpid ()) < 0 ) {
    perror ("fcntl ( s, F_SETOWN )");
    exit (1);
  }

  len = sizeof ( sa );
  sa.sun_family = AF_UNIX;
  strcpy ( sa.sun_path, UN_PATH );
  if ( bind ( srv, ( struct sockaddr * )&sa, len ) < 0 ) {
    perror ("bind ()");
    exit (1);
  }
  fprintf ( stderr, "bind () OK\n");

  if ( listen ( srv, 2 * cli_num + 3 ) < 0 ) {
    perror("listen ()");
    exit (1);
  }
  fprintf ( stderr, "listen () OK\n");

  pfd[0].fd = srv;
  pfd[0].events = POLLRDNORM;
  cli_now = 0;
  
  fprintf ( stderr, "Initializing loop:");
  for ( int i = 1; i < cli_num; i++ ) { 
    fprintf ( stderr, "." );
    pfd[i].fd = -1;
  }  
  fprintf ( stderr, "\nEntering loop\n");
  for ( ;; ) {
    n = poll ( pfd, cli_now + 1, -1 ); // no tmo
    fprintf ( stderr, "Aha!\n");
    if ( pfd[0].revents & POLLRDNORM ) { // new client
		  if ( cli_now < cli_num ) {
        if (( cli = accept ( srv, NULL, NULL )) < 0 ) perror ("accept()");
  		  else {
  		    fprintf ( stderr, "accept() OK\n: " );
#if 0
          for ( int i = 1; i < cli_num; i++ ) { 
            if ( pfd[i].fd == -1 ) { 
              pfd[i].fd = cli;
              pfd[i].events = POLLRDNORM;
              cli_now++;
              fprintf ( stderr, "client#%d\n", cli_now );
              break;
            }
          }
#else
          pfd[++cli_now].fd = cli;
          pfd[cli_now].events = POLLRDNORM;
          fprintf ( stderr, "client#%d\n", cli_now );
#endif          
        }
      }
      else fprintf ( stderr, "Too many clients\n" );
      if ( n == 1 ) continue;
    }
    for ( int i = 1; i < cli_num; i++ ) { 
//fprintf ( stderr, "." );
      if (( cli = pfd[i].fd ) < 0 ) continue;   
//      fprintf ( stderr, "pfd[%d].revents=%X\n", i, pfd[i].revents );
      if ( pfd[i].revents & ( POLLRDNORM | POLLERR )) {
        l = read ( cli, buf, sizeof ( buf ));
        if ( l < 0 ) {
          if ( errno == ECONNRESET ) {   // connection reset by client
            close ( cli );
            pfd[i].fd = -1;    
            cli_now--;
            fprintf ( stderr, "connection reset by client\n" );
          }
          else perror ("read()");
        }
        else if ( l == 0 ) {
          close ( cli );
#if 0
          pfd[i].fd = -1;
#else
          if ( i < cli_now ) {
            memcpy ( &pfd[i], &pfd[cli_now], sizeof ( pollfd ));
            pfd[cli_now].fd = -1;
          }    
#endif
          cli_now--;
          fprintf ( stderr, "connection closed by client\n" );
        }
        else {
          buf[l++] = '\n';
          buf[l] = 0;
          fprintf ( stderr, "%s", buf );
        }
        if ( --n <= 0 ) break;
      }
    }
  }
/* not reached */
  return 0;
}