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Date:	Mon, 17 Sep 2012 15:42:14 +0200
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Subject:	Re: Win PTY library.
From:	=?UTF-8?Q?V=C3=A1clav_Zeman?= <vhaisman AT gmail DOT com>
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On 17 September 2012 15:27, Charles Wilson wrote:
>
> On 9/17/2012 7:03 AM, Daniel Colascione wrote:
> > On 9/15/2012 9:21 AM, Christopher Faylor wrote:
> >> On Sat, Sep 15, 2012 at 12:15:49PM -0400, Earnie Boyd wrote:
> >>> I just discovered https://github.com/rprichard/winpty and thought
> >>> Cygwin users and developers may be interested.  The license is MIT
> >>> style.
> >>
> >> Looks interesting.  I've had something similar sitting around in my
> >> Cygwin sandbox for a while.  It would be nice to have a real
> >> console-based
> >> pty implementation.
> >
> > Unfortunately, this program works by polling and scraping a hidden
> > console
> > window. Any approach of this type will lose data. (No, you can't
> > synchronize
> > your scraping by using console accessibility APIs because conhost calls
> > out into
> > accessibility with its locks held, and if you try to read the console
> > buffer in
> > this context, you deadlock.)
>
> Well, that's exactly what Console2 does, and it works pretty well. I've
> never seen any "missing" data when using it. I don't know what they're
> doing to work around the deadlock issue, but whatever it is it works.

I think that the difference is that PTY is a stream of commands that get
interpreted, OTOH, polled Windows console can provide only a snapshot at
some point in time. It seems that it would be hard to produce faithful
stream of commands from this console snapshot. Because Console2 is only
visualizing the snapshot in its own GUI window, it does not matter that it
is doing that by snapshotting the hidden console. But for the PTY
abstraction, a faithful chain of commands seems necessary. I think that any
such polling based implementation could miss some transitions in the PTY
state in between the polls.

--
VZ

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