Poll Not recognizing Socket.

Poll Not recognizing Socket.

Post by Scott Wachtle » Thu, 09 Mar 2000 04:00:00

  I'm trying to use poll in a socket program, but it doesn't seem to
recognize with then is a connection on a particular socket. I've
attached a "sample" program below which sort of illustrates my problem.
Poll never returns with a POLLNORM.
  Must I use accept to create a filedescriptor first? If so, how do I
avoid blocking, so that other filedescriptors also get checked? The Poll
man page seems to imply that polling should work after a listen is
  Any help is appreciated.

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <poll.h>
#include <fcntl.h>
#include <fcntl.h>

#include <netinet/in.h>
#include <sys/socket.h>

void main(){

 int s;
  struct pollfd poll_cli[2];
  struct sockaddr_in saun;
   int len,result;

 perror("server: socket");

saun.sin_family= AF_INET;
saun.sin_port = htons(38320);
saun.sin_addr.s_addr = htonl(INADDR_ANY);

len = sizeof(saun);
if(bind(s,(struct sockaddr*)&saun,len)<0){
 perror("server: bind");

 perror("server: listen");

poll_cli[0].fd = s;
poll_cli[0].events == POLLNORM;


   if(result >0){

    printf("Activity on socket\n");
   if(poll_cli[0].revents == POLLNORM){   /* Never True */
      printf(" POLLNORM \n");



1. poll() not reporting POLLHUP's on sockets?

On SunOS 5.6/5.7, I run a poll() for POLLIN conditions on a
socket obtained through the following sequence:

socket(AF_INET, SOCK_STREAM, 0) ->
-> bind(...) -> listen(...) -> accept(...)

The client connects through a matching sequence:

socket(...) -> connect(...)

My problem is, when the client shuts down:

shutdown(...) -> close(...) -> exit(...)

the poll() call on the server returns, but the "revents" field
for the socket concerned is set to be POLLIN, not the
POLLHUP I would expect.

Similarly, when I poll() for conditions POLLIN | POLLRDNORM,
I get POLLIN | POLLRDNORM back when the socket is shut
by the client.

When I try to read() from the socket in either case, it
returns 0, not -1, and errno remains 0.

This behavior seems abnormal; any ideas?

Zheng-Zheng Zhou

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