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Date: Wed, 19 Nov 2008 15:02:50 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: rsync 3.0.4 over ssh hanging on cygwin 1.7
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On Nov 19 07:24, Brett Serkez wrote:
> On Wed, Nov 19, 2008 at 6:54 AM, Fred Kemp <c DOT f DOT kemp AT reading DOT ac DOT uk> wrote:
> > In the meantime, if anyone has any ideas as to where the problem lies, I
> > would be willing to spend some time investigating it further. It does seem
> > to be a longstanding issue, with posts as far back as 2002 and as recent as
> > last month on the subject.
> 
> I spent considerable time on this and reported were the problem is
> occurring to no avail, don't waste your time.  In a nutshell the issue
> is with Cygwin's bi-directional pipe emulation, this is a fundamental

Pipes are uni-directional.

> feature of all UNIXies.  Secure Shell "forks and execs" rsync,
> connecting standard out and in so that data flows over the internet
> to/from SSH and then locally to/from rsync.  The problem is that
> eventually a "signal" is missed and SSH and rsync deadlock, the local
> pipe emulation is imperfect, and the rsync protocol has no provision
> to recover from this dead lock.
> 
> A fix would require a change to this fundamental feature of Cygwin, it
> is not clear to me that Windows has the necessary functionality to
> properly implement, such a fix would require extensive retesting.

Efforts have been made to rectify this problem (most notably by Bob Byrnes
and cgf) but the right fix/hack/workaround hasn't been found yet.  There's
always a border situation in which the the NT kernel seems to refuse to
give the required information back to the application.

Patches are *extremly* thoughtfully considered in this case...


Corinna

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

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