[reSIProcate] unresponsive DNS query blocks stack thread if USE_IPV6 is not defined (windows)

[Justin Matthews]

Nice catch, thanks.  Let me know if you have any further issues with this.

 

-justin

 

From: Kennard White [mailto:kennard_white at logitech.com] 
Sent: Wednesday, November 10, 2010 4:10 PM
To: Justin Matthews
Cc: resiprocate-devel
Subject: Re: [reSIProcate] unresponsive DNS query blocks stack thread if
USE_IPV6 is not defined (windows)

 

Hey guys,

I think I figured out why the code was setup for blocking under linux. There
is a bug in the linux implementation of ares make_socket_non_blocking(). The
line:
               if (fcntl(s, F_GETFL, &flags) == -1)
should be:
               if ( (flags  = fcntl( fd, F_GETFL, 0)) == -1 )

Reference rutil/Socket.cxx for comparison. (Though that function is missing
the error checking).

Because of above bug, the set to nonblocking would fail under linux. Someone
must have worked around this by getting rid of the nonblocking completely.

I didn't include patch since one-line fix.

Thanks,
Kennard

On Mon, Nov 1, 2010 at 7:34 AM, Justin Matthews <jmatthewsr at gmail.com>
wrote:

Updated ares_process.c to set UDP sockets non-blocking for build
configurations where they were previously blocking:

 

.         Windows where USE_IPV6 was not defined

.         All non-windows builds

 

-justin

 

From: slgodin at gmail.com [mailto:slgodin at gmail.com] On Behalf Of Scott Godin
Sent: Friday, October 29, 2010 8:05 PM
To: Justin Matthews
Cc: resiprocate-devel
Subject: Re: [reSIProcate] unresponsive DNS query blocks stack thread if
USE_IPV6 is not defined (windows)

 

After a quick look, seems odd to me as well.  Also if non-windows we never
set the UDP socket to non-blocking.  What I don't get is why people on linux
have not noticed a blocking problem yet.  TCP DNS sockets seem to be set as
non-blocking properly for linux and windows both with and without the
USE_IPV6 directive.

 

Scott

On Fri, Oct 29, 2010 at 10:52 AM, Justin Matthews <jmatthewsr at gmail.com>
wrote:

Hi,

Does anyone know if it's intended behavior for the ares UDP socket to block
if USE_IPV6 is not defined (Windows OS)?  In ares_process.c ,
open_udp_socket() will set the socket non-blocking only if USE_IPV6 is
defined.  If DNS is misconfigured or there is no response for a DNS record
lookup, the resip stack thread will block indefinitely in the recv() call in
read_udp_packets().

Thanks,

-justin

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