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Date: Wed, 19 Nov 2008 09:54:41 -0500
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
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Subject: Re: rsync 3.0.4 over ssh hanging on cygwin 1.7
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On Wed, Nov 19, 2008 at 07:24:33AM -0500, Brett Serkez wrote:
>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
>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.

Your analysis of the problem is likely incorrect.  The problem has been
reported to be due to the fact that there is no foolproof way in Windows
to tell when a pipe can be written to in a non-blocking fashion.  Since
that fact hasn't changed, I doubt that this has anything to do with
missed "signal"s and it certainly doesn't have anything to do with
bidirectional pipes.

Nevertheless, the problem is still there and as always PGA.  I have
spent a considerable amount of time staring at the code and googling for
a solution but to no avail.

cgf

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