1.7.7 blocking socket problem

Corinna Vinschen corinna-cygwin@cygwin.com
Wed Nov 17 17:51:00 GMT 2010

On Nov 17 11:20, Mark Rivers wrote:
> Folks,
> I believe I have discovered a problem with blocking sockets on Cygwin.
> The problem is that very rarely a call to send() will never return.
> I am having problem when using the Channel Access TCP/IP protocol in the
> EPICS control system (http://www.aps.anl.gov/epics/).
> I have isolated the problem to a call to send() on the server which
> never returns.  This problem happens with a large number of well-tested
> clients, running on both Linux and Windows.  I can build the same EPICS
> server without Cygwin, using the MS VC++ Windows compiler and libraries
> and it does not fail.  When the call to send() hangs it is sending a
> large packet (just over 8KB).  The failure rate is very low, perhaps
> once in 10 million calls to send().

Wow, that's not very often.  You missed all the stuff from
http://cygwin.com/problems.html, so we don't know what Cygwin release
you're talking about.  If it's Cygwin 1.5, you're out of luck since we
don't support that anymore.  Otherwise...

> I realize that my application is difficult to reproduce for the Cygwin
> developers.  I am willing to try to write a simple socket server and
> client to try to reproduce the problem in a simple test setup. 

...that would be most helpful.

> But
> before I do that I would like to first know if there is a known problem
> of this sort that has already been reported, and perhaps fixed.

No, not really.  I wouldn't claim that Cygwin's socket implementation is
bug free, but this kind of very occassional hang is new to me.


Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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