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Date: Thu, 10 Oct 2013 03:29:36 -0400
From: Don Hatch <hatch AT plunk DOT org>
To: cygwin AT cygwin DOT com
Cc: Don Hatch <hatch AT plunk DOT org>
Subject: Re: ssh takes forever to interrupt-- known problem?
Message-ID: <20131010072936.GA29937@plunk.org>
References: <20131009221915 DOT GA6345 AT plunk DOT org> <5255DAD2 DOT 5000707 AT cygwin DOT com> <20131009225852 DOT GA8151 AT plunk DOT org> <20131009232140 DOT GA9487 AT plunk DOT org> <5255E722 DOT 40008 AT cygwin DOT com> <20131010004449 DOT GA13071 AT plunk DOT org> <5256164E DOT 2010606 AT cygwin DOT com>
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On Wed, Oct 09, 2013 at 10:51:58PM -0400, Larry Hall (Cygwin) wrote:
> OK, I'm going to assume that 'sshd' was actually started when
> you tried the latest rounds of tests.  If this wasn't the case, you have
> another (probably non-Cygwin) SSH server running which is causing the
> problem.  You'll need to shut that service down and start the Cygwin
> one before trying again.

Right, if I want to connect to sshd on the windows machine,
I start the cygwin sshd manually if I haven't already.
However I can reproduce the problem with no cygwin sshd running at all,
by ssh'ing from the cygwin/windows machine to a linux machine.

> 
> Beyond that, you could try invoking invoking 'yes' through 'strace' and
> see if the output there gives you any clues.

Tried that, on the linux machine I was ssh'ed into.
What I found was:
    - if I ctrl-c approximately 1/8 to 1/4 second after starting "yes",
      the program receives it and is killed 2.5 seconds later,
      but the output (about 62558 bytes of "y\n"s)
      takes 30 seconds more to finish spewing.
    - if I ctrl-c approximately 1 second after starting "yes",
      the program receives it and is killed 5.25 seconds later,
      but the output (about 119278 bytes of "y\n"s)
      takes 57 seconds more to finish spewing.

So I'm thinking there's a buffer somewhere in all this
that is (too) capable of quickly recieving and buffering a whole lot of data,
but there's a bottleneck somewhere after that buffer
that makes it take a long time for the data to dribble out to the terminal.
I wonder where that buffer is, and if there's a way to decrease
the buffer size so that output-bound programs will block sooner,
for decreased throughput and increased interactivity,
which would be what I want, I think.
      
> You could also try cutting
> down your path to eliminate potential interactions.

I straced ssh when ssh'ing into the linux box...
no programs were run other than c:\cygwin\bin\ssh.exe
so that eliminates that possibility, right?

> try adding "detect_bloda" to your Cygwin environment variable to see if
> it points to some conflicting program/service:
> 
> <http://cygwin.com/cygwin-ug-net/using-cygwinenv.html#cygwinenv-implemented-options>

Tried setting env CYGWIN=detect_bloda
and ran ssh again, didn't see anything different (although I'm not sure exactly
what I should expect to see if it detects something fishy).

> 
> If those don't provide any clues, I'm out of ideas. :-(
> 
Hope not :-)  I appreciate your eyes on this.

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