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Date: Thu, 14 Apr 2011 19:21:26 +0100
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Subject: Re: 1.7.9-1: typeahead queue not flushed when Ctrl+C pressed
From: Andy Koppe <andy DOT koppe AT gmail DOT com>
To: cygwin AT cygwin DOT com
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On 4 April 2011 19:39, Edward McGuire wrote:
> When I type ahead in an uncustomized terminal window, I expect my
> keyboard input to be queued until it is called for. When I press
> Ctrl+C, I expect the queue to be flushed. Any keyboard input still
> in the queue should be lost.
>
> The trouble I am having is that my keyboard input is preserved when
> I press Ctrl+C. I can easily reproduce the problem with the
> following keyboard input at a bash prompt:
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0$ tail -f /dev/null [Enter]
> =C2=A0 =C2=A0 =C2=A0 =C2=A0[Enter]
> =C2=A0 =C2=A0 =C2=A0 =C2=A0[Enter]
> =C2=A0 =C2=A0 =C2=A0 =C2=A0[Enter]
> =C2=A0 =C2=A0 =C2=A0 =C2=A0[Ctrl+C]
>
> If the typeahead queue is flushed by the Ctrl+C, then a bash prompt
> will appear. But if the queue is not flushed, then four bash prompts
> will appear. In my case, four bash prompts appear.
>
> I have reproduced the problem in a Cygwin (cmd.exe) window, in a
> mintty window, and in an xterm window.
>
> There is a termio mode bit, NOFLSH, which disables flush after
> interrupt. If this bit were set, it would explain why I am having
> the problem. But "stty -a" shows that this mode bit is not set. I
> checked this bit before and after reproducing the problem.
>
> I was still able to reproduce the problem after setting and clearing
> the NOFLSH bit with "stty noflsh; stty -noflsh".
>
> I have attached the output of "stty -a" below, along with the output
> of "cygcheck -s -v -r" and of "cat /var/log/xwin/XWin.0.log".
>
> I have not found this problem mentioned on the Cygwin list.
>
> Where might I be going wrong? Is this a limitation of the Cygwin
> termio?

Yep, looks like the NOFLSH bit is ignored. There's no mention of it in
the Cygwin sources except in sys/termios.h.

Have you confirmed that it behaves as expected on Linux?

> ...
> $ cygcheck -s -v -r [note: value of svnroot and SVN_SSH variables redacte=
d]
> ...

Thanks for providing this, but it's supposed to be attached rather
than included.

Andy

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