bug report: poll() with listen sockets always gives POLLERR

bug report: poll() with listen sockets always gives POLLERR

[Steven O'Brien]

Hi

The current implementation of poll() does not behave correctly with
listen sockets. It always gives a POLLERR revent when a connection
request is received. I believe the error is in poll.cc lines 96-108:
        switch (sock->recvfrom (peek, sizeof (peek), MSG_PEEK,
                                NULL, NULL))
          {
            case -1: /* Something weird happened */
              fds[i].revents |= POLLERR; 
              break;
            case 0:  /* Closed on the read side. */
              fds[i].revents |= POLLHUP;
              break;
            default:
              fds[i].revents |= POLLIN;
              break;
          }

the recvfrom call always returns -1 for a listen socket, and so we
always get POLLERR. I could not see an easy way of detecting a listen
socket at this point in the code, since the fhandler_socket class
records listen and connected sockets as the same thing (type ==
CONNECTED).

Because glib uses poll() to detect connection requests in a server, all
glib-based servers now fail in cygwin. I guess most cygwin ported
servers must be using select() rather than poll() as this behaviour
first appeared in cygwin 1.3.13-1 but has not been reported to the list
until now.

My apologies for not providing a patch, but hopefully someone with
better knowledge of cygwin internals will be able to detect a listen
socket in the above code and provide a special case for it.

Regards,
  Steven


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Re: bug report: poll() with listen sockets always gives POLLERR

[Corinna Vinschen]

On Tue, Nov 19, 2002 at 01:34:30PM +0000, Steven O'Brien wrote:
> Hi
> 
> The current implementation of poll() does not behave correctly with
> listen sockets. It always gives a POLLERR revent when a connection
> request is received. I believe the error is in poll.cc lines 96-108:
> [...]

Thanks for the report.  I've checked in a patch.  Please try the
next developers snapshot.

Corinna

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Re: bug report: poll() with listen sockets always gives POLLERR

[Corinna Vinschen]

On Wed, Nov 20, 2002 at 09:07:30AM +0000, Steven O'Brien wrote:
> Corinna Vinschen wrote:
> 
> > On Tue, Nov 19, 2002 at 01:34:30PM +0000, Steven O'Brien wrote:
> > > Hi
> > > 
> > > The current implementation of poll() does not behave correctly with
> > > listen sockets. It always gives a POLLERR revent when a connection
> > > request is received. I believe the error is in poll.cc lines 96-108:
> > > [...]
> 
> > Thanks for the report.  I've checked in a patch.  Please try the
> > next developers snapshot.
> 
> > Corinna
> 
> Thanks Corinna, but its still not quite right. poll() needs to set
> POLLIN

Oops, sure.  Thanks, I've applied the patch.

Corinna

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Re: bug report: poll() with listen sockets always gives POLLERR

[Steven O'Brien]

Corinna Vinschen wrote:

> On Tue, Nov 19, 2002 at 01:34:30PM +0000, Steven O'Brien wrote:
> > Hi
> > 
> > The current implementation of poll() does not behave correctly with
> > listen sockets. It always gives a POLLERR revent when a connection
> > request is received. I believe the error is in poll.cc lines 96-108:
> > [...]

> Thanks for the report.  I've checked in a patch.  Please try the
> next developers snapshot.

> Corinna

Thanks Corinna, but its still not quite right. poll() needs to set
POLLIN
when a connection request is received on a listen socket. The following
patch completes the job:

--- poll.cc	2002-11-20 08:57:03.000000000 +0000
+++ poll.cc-fix	2002-11-20 09:01:21.000000000 +0000
@@ -111,9 +111,12 @@ poll (struct pollfd *fds, unsigned int n
 				 Unfortunately, recvfrom() doesn't make much
 				 sense then.  It returns WSAENOTCONN in that
 				 case.  Since that's not actually an error,
-				 we must not set POLLERR. */
+				 we must not set POLLERR, but POLLIN to
+				 indicate the request. */
 			      if (WSAGetLastError () != WSAENOTCONN)
 				fds[i].revents |= POLLERR;
+			      else
+			        fds[i].revents |= POLLIN;
 			      break;
 			    case 0:  /* Closed on the read side. */
 			      fds[i].revents |= POLLHUP;

Regards,
 Steven

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