pty issue causes 'screen' to hang when run from mintty as detached

pty issue causes 'screen' to hang when run from mintty as detached

[Matt D.]

See here for additional information and reproducible steps in the mintty 
support ticket:
https://code.google.com/p/mintty/issues/detail?id=390

I can reproduce this using cygwin 1.7.20, 1.7.19, 1.7.18, 1.7.15, and 1.7.7.

Screen does NOT hang when is is created by calling the first command 
through cygwin started by cygwin.bat (commands typed through Windows 
terminal 'cmd.exe' instead of mintty) and then attempting to attach 
through mintty with the second command.

Workaround is to use:

'cygstart --hide screen -S name -d -m'

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Andrew Schulman]

> See here for additional information and reproducible steps in the mintty 
> support ticket:
> https://code.google.com/p/mintty/issues/detail?id=390
> 
> I can reproduce this using cygwin 1.7.20, 1.7.19, 1.7.18, 1.7.15, and 1.7.7.
> 
> Screen does NOT hang when is is created by calling the first command 
> through cygwin started by cygwin.bat (commands typed through Windows 
> terminal 'cmd.exe' instead of mintty) and then attempting to attach 
> through mintty with the second command.
> 
> Workaround is to use:
> 
> 'cygstart --hide screen -S name -d -m'

I get a little different result:

$ screen -S scrn -d -m
$ screen -S name -x
Remove dead screens with 'screen -wipe'.
$

and then I have to run 'reset' to get input echoing back.

I've never observed this behavior before, because I always start screen as
'screen -AURD', which works fine.

Do we have any idea whether the problem is with mintty or with screen?  Either
way, I'm afraid I'm not likely to be much help, except that an update of screen
might fix the problem.  The version of screen in Cygwin (4.0.3) hasn't been
updated in several years, because there's a big Cygwin-specific patch that will
have to be either merged into recent screen code, or be determined to be no
longer needed.

Andrew


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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Andrew Schulman]

> $ screen -S name -d -m
> $ screen -S name -x
> Remove dead screens with 'screen -wipe'.
> $

Sorry, typed by hand, corrected above.


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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Matt D.]

If you read the response from the mintty author in the support ticket 
linked in the original post you'll see:

"There've been various issues with pseudo terminal (pty) layer in the 
Cygwin 1.7.19 release, which apparently haven't been fully addressed in 
1.7.20. Mintty is based on that pty layer, along with other terminals 
such as rxvt or xterm, whereas the Windows console window you get 
through cygstart is not."

I've tested it with several versions of Cygwin all the way back to 1.7.7.

It might be worth following up with the author through the support 
ticket yourself, as he seems to believe that the error lies with 
Cygwin's pty and cannot be fixed in mintty.


On 6/10/2013 10:53 PM, Andrew Schulman wrote:
>> $ screen -S name -d -m
>> $ screen -S name -x
>> Remove dead screens with 'screen -wipe'.
>> $
>
> Sorry, typed by hand, corrected above.
>
>
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>

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Greg Turner]

On Wed, Jun 12, 2013 at 3:19 PM, Matt D. <matt@codespunk.com> wrote:
> "the Windows console window you get through cygstart is not [a pty]"

Ah, so /that's/ what I recently read uncomprehendingly!  Thanks for
tracking down this concise explanation.  Assuming that's right, then,
I wonder: what is it?

-gmt

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Larry Hall (Cygwin)]

On 6/13/2013 3:34 PM, Greg Turner wrote:
> On Wed, Jun 12, 2013 at 3:19 PM, Matt D. <matt@codespunk.com> wrote:
>> "the Windows console window you get through cygstart is not [a pty]"
>
> Ah, so /that's/ what I recently read uncomprehendingly!  Thanks for
> tracking down this concise explanation.  Assuming that's right, then,
> I wonder: what is it?

What is what?  This Windows console?  It's... well, it's a... um, it's
a Windows console! ;-)

But seriously, it's just something different that doesn't conform to
the definition of a PTY.  Windows doesn't have PTYs.  It uses the
console instead.

-- 
Larry

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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RE: pty issue causes 'screen' to hang when run from mintty as detached

[gmt]

On Thu, 13 Jun 2013, at 14:07, Larry Hall (Cygwin) thusly quipped:

> On 6/13/2013 3:34 PM, Greg Turner wrote:
>> On Wed, Jun 12, 2013 at 3:19 PM, Matt D. <matt@codespunk.com> wrote:
>>> "the Windows console window you get through cygstart is not [a pty]"
>> 
>> Ah, so /that's/ what I recently read uncomprehendingly!  Thanks for
>> tracking down this concise explanation.  Assuming that's right, then,
>> I wonder: what is it?
> 
> What is what?  This Windows console?  It's... well, it's a... um, it's a
Windows
> console! ;-)
> 
> But seriously, it's just something different that doesn't conform to the
> definition of a PTY.  Windows doesn't have PTYs.  It uses the console
instead.

So, no win32-console-specific fhandler exists, and clones of the win32 stdio
handles are simply passed through cygwin core to newlib and vice-versa
without any funny-business?

-gmt



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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Larry Hall (Cygwin)]

On 6/13/2013 7:39 PM, gmt@malth.us wrote:
> On Thu, 13 Jun 2013, at 14:07, Larry Hall (Cygwin) thusly quipped:
>
>> On 6/13/2013 3:34 PM, Greg Turner wrote:
>>> On Wed, Jun 12, 2013 at 3:19 PM, Matt D. <matt@codespunk.com> wrote:
>>>> "the Windows console window you get through cygstart is not [a pty]"
>>>
>>> Ah, so /that's/ what I recently read uncomprehendingly!  Thanks for
>>> tracking down this concise explanation.  Assuming that's right, then,
>>> I wonder: what is it?
>>
>> What is what?  This Windows console?  It's... well, it's a... um, it's a
> Windows
>> console! ;-)
>>
>> But seriously, it's just something different that doesn't conform to the
>> definition of a PTY.  Windows doesn't have PTYs.  It uses the console
> instead.
>
> So, no win32-console-specific fhandler exists, and clones of the win32 stdio
> handles are simply passed through cygwin core to newlib and vice-versa
> without any funny-business?

I don't really grok what you mean by "funny-business"  But let me say
this.  Cygwin knows how to communicate with Windows consoles.  The code
is in fhandler_console.cc if you want to look at it.  But there is a
mismatch in capabilities and expectations between ptys and the Windows
console API.  That's why there is also fhandler_tty.cc.  The former does
its best to match the Linux/Unix world's expectations to what the Windows
console can provide (which is pretty limited).  The latter simply sidesteps
the console and provides better pty support.

-- 
Larry

_____________________________________________________________________

A: Yes.
 > Q: Are you sure?
 >> A: Because it reverses the logical flow of conversation.
 >>> Q: Why is top posting annoying in email?

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Andy Koppe]

On 11 June 2013 01:51, Andrew Schulman wrote:
>> See here for additional information and reproducible steps in the mintty
>> support ticket:
>> https://code.google.com/p/mintty/issues/detail?id=390
>>
>> I can reproduce this using cygwin 1.7.20, 1.7.19, 1.7.18, 1.7.15, and 1.7.7.
>>
>> Screen does NOT hang when is is created by calling the first command
>> through cygwin started by cygwin.bat (commands typed through Windows
>> terminal 'cmd.exe' instead of mintty) and then attempting to attach
>> through mintty with the second command.
>>
>> Workaround is to use:
>>
>> 'cygstart --hide screen -S name -d -m'
>
> I get a little different result:
>
> $ screen -S scrn -d -m
> $ screen -S name -x
> Remove dead screens with 'screen -wipe'.
> $
>
> and then I have to run 'reset' to get input echoing back.
>
> I've never observed this behavior before, because I always start screen as
> 'screen -AURD', which works fine.
>
> Do we have any idea whether the problem is with mintty or with screen?

I observed the same behaviour as the OP, but also reproduced it in
rxvt and xterm, so not a mintty issue. Since it works in a console,
the Cygwin pty layer has to be the main suspect, unless screen has
specfic code for Cygwin consoles or ptys?

Andy

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Corinna Vinschen]

On Jun 14 12:57, Andy Koppe wrote:
> On 11 June 2013 01:51, Andrew Schulman wrote:
> >> See here for additional information and reproducible steps in the mintty
> >> support ticket:
> >> https://code.google.com/p/mintty/issues/detail?id=390
> >>
> >> I can reproduce this using cygwin 1.7.20, 1.7.19, 1.7.18, 1.7.15, and 1.7.7.
> >>
> >> Screen does NOT hang when is is created by calling the first command
> >> through cygwin started by cygwin.bat (commands typed through Windows
> >> terminal 'cmd.exe' instead of mintty) and then attempting to attach
> >> through mintty with the second command.
> >>
> >> Workaround is to use:
> >>
> >> 'cygstart --hide screen -S name -d -m'
> >
> > I get a little different result:
> >
> > $ screen -S scrn -d -m
> > $ screen -S name -x
> > Remove dead screens with 'screen -wipe'.
> > $
> >
> > and then I have to run 'reset' to get input echoing back.
> >
> > I've never observed this behavior before, because I always start screen as
> > 'screen -AURD', which works fine.
> >
> > Do we have any idea whether the problem is with mintty or with screen?
> 
> I observed the same behaviour as the OP, but also reproduced it in
> rxvt and xterm, so not a mintty issue. Since it works in a console,
> the Cygwin pty layer has to be the main suspect, unless screen has
> specfic code for Cygwin consoles or ptys?

If this can really be reproduced back to Cygwin 1.7.7, it's a rather
long-standing problem.  Did anybody try to track this down at one point?


Corinna

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Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Andrew Schulman]

> > Do we have any idea whether the problem is with mintty or with screen?
> 
> I observed the same behaviour as the OP, but also reproduced it in
> rxvt and xterm, so not a mintty issue. Since it works in a console,
> the Cygwin pty layer has to be the main suspect, unless screen has
> specfic code for Cygwin consoles or ptys?

I don't think so, but there's one big, crufty old patch that I had to use to get
screen to run a few years ago.

The version of screen that we're using now in Cygwin, 4.0.3, is about 8 years
old.  There haven't been any official new releases since then, but development
has continued and there have been a lot of improvements.  I'm in the process of
building an updated package from the latest git, and that version appears not to
need any of the patches I used to have to use to get screen to compile and run
in Cygwin.

So, I suggest that we wait until the new screen test release comes out, within a
few days, and see if that fixes the problem.


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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Christopher Faylor]

On Mon, Jun 17, 2013 at 06:08:27AM -0400, Andrew Schulman wrote:
>> > Do we have any idea whether the problem is with mintty or with screen?
>> 
>> I observed the same behaviour as the OP, but also reproduced it in
>> rxvt and xterm, so not a mintty issue. Since it works in a console,
>> the Cygwin pty layer has to be the main suspect, unless screen has
>> specfic code for Cygwin consoles or ptys?
>
>I don't think so, but there's one big, crufty old patch that I had to use to get
>screen to run a few years ago.
>
>The version of screen that we're using now in Cygwin, 4.0.3, is about 8 years
>old.  There haven't been any official new releases since then, but development
>has continued and there have been a lot of improvements.  I'm in the process of
>building an updated package from the latest git, and that version appears not to
>need any of the patches I used to have to use to get screen to compile and run
>in Cygwin.
>
>So, I suggest that we wait until the new screen test release comes out, within a
>few days, and see if that fixes the problem.

I looked at this briefly over the weekend and saw a problem in Cygwin's
pty handling code.  I don't know exactly what the problem is yet but there
is something not quite right there.  Something is closing a windows handle
and that's causing a SIGHUP to be sent to the pty owner.  That's not right.

I'll fix this problem eventually but it will be interesting to see if a
newer screen behaves any better.

cgf

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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Andrew Schulman]

> On Mon, Jun 17, 2013 at 06:08:27AM -0400, Andrew Schulman wrote:
> >> > Do we have any idea whether the problem is with mintty or with screen?
> >> 
> >> I observed the same behaviour as the OP, but also reproduced it in
> >> rxvt and xterm, so not a mintty issue. Since it works in a console,
> >> the Cygwin pty layer has to be the main suspect, unless screen has
> >> specfic code for Cygwin consoles or ptys?
> >
> >I don't think so, but there's one big, crufty old patch that I had to use to get
> >screen to run a few years ago.
> >
> >The version of screen that we're using now in Cygwin, 4.0.3, is about 8 years
> >old.  There haven't been any official new releases since then, but development
> >has continued and there have been a lot of improvements.  I'm in the process of
> >building an updated package from the latest git, and that version appears not to
> >need any of the patches I used to have to use to get screen to compile and run
> >in Cygwin.
> >
> >So, I suggest that we wait until the new screen test release comes out, within a
> >few days, and see if that fixes the problem.
> 
> I looked at this briefly over the weekend and saw a problem in Cygwin's
> pty handling code.  I don't know exactly what the problem is yet but there
> is something not quite right there.  Something is closing a windows handle
> and that's causing a SIGHUP to be sent to the pty owner.  That's not right.
> 
> I'll fix this problem eventually but it will be interesting to see if a
> newer screen behaves any better.

No, I just tested it on the latest screen release, and the problem still occurs.


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Re: pty issue causes 'screen' to hang when run from mintty as detached

[Christopher Faylor]

On Mon, Jun 17, 2013 at 09:58:35AM -0400, Christopher Faylor wrote:
>On Mon, Jun 17, 2013 at 06:08:27AM -0400, Andrew Schulman wrote:
>>> > Do we have any idea whether the problem is with mintty or with screen?
>>> 
>>> I observed the same behaviour as the OP, but also reproduced it in
>>> rxvt and xterm, so not a mintty issue. Since it works in a console,
>>> the Cygwin pty layer has to be the main suspect, unless screen has
>>> specfic code for Cygwin consoles or ptys?
>>
>>I don't think so, but there's one big, crufty old patch that I had to use to get
>>screen to run a few years ago.
>>
>>The version of screen that we're using now in Cygwin, 4.0.3, is about 8 years
>>old.  There haven't been any official new releases since then, but development
>>has continued and there have been a lot of improvements.  I'm in the process of
>>building an updated package from the latest git, and that version appears not to
>>need any of the patches I used to have to use to get screen to compile and run
>>in Cygwin.
>>
>>So, I suggest that we wait until the new screen test release comes out, within a
>>few days, and see if that fixes the problem.
>
>I looked at this briefly over the weekend and saw a problem in Cygwin's
>pty handling code.  I don't know exactly what the problem is yet but there
>is something not quite right there.  Something is closing a windows handle
>and that's causing a SIGHUP to be sent to the pty owner.  That's not right.
>
>I'll fix this problem eventually but it will be interesting to see if a
>newer screen behaves any better.

This problem should be fixed in the upcoming snapshot.

It was a longstanding bug in the pty code.

Thanks for providing the succinct steps required to duplicate the
problem.

cgf

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