bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Steve Purcell]

I've been investigating an issue with magit in Emacs HEAD which isn't
present in Emacs 23.x. Specifically, the git subprocesses it starts in
order to pipe data to them do not exit as expected when magit calls
process-send-eof.

Further investigation shows that this misbehavior can be demonstrated by
executing the following simple code in *scratch*:

(let ((p (start-process "cat" (current-buffer) "cat")))
  (process-send-eof p)
  (sit-for 1)
  (process-status p))

In Emacs 23, the result is 'exit, and "Process cat finished" is written
into the buffer.

In Emacs HEAD, however, the result is 'run, and "^D" is written into the
buffer - obviously the process' input is not really being closed.

This incorrect behavior happens regardless of the value of
process-connection-type.

More discussion of this issue in the context of magit is to be found
here: http://github.com/philjackson/magit/issues/#issue/18




In GNU Emacs 24.0.50.1 (x86_64-apple-darwin10.4.0, NS apple-appkit-1038.32)
of 2010-08-01 on mandala.home
Windowing system distributor `Apple', version 10.3.1038
configured using `configure  '--with-ns' '--without-dbus' 'CFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: nil
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  shell-dirtrack-mode: t
  paredit-mode: t
  show-paren-mode: t
  eldoc-mode: t
  diff-auto-refine-mode: t
  cua-mode: t
  desktop-save-mode: t
  global-auto-complete-mode: t
  auto-complete-mode: t
  ido-everywhere: t
  recentf-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  unify-8859-on-decoding-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:

Recent messages:
Undo!
run [2 times]
byte-code: End of buffer [2 times]
Killed line
Saving file /Users/steve/Desktop/foo...
Wrote /Users/steve/Desktop/foo
help-setup-xref: Symbol's value as variable is void: help-xref-following
Auto-saving...done
t
Auto-saving...done

Load-path shadows:
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/Users/steve/.emacs.d/site-lisp/rinari/util/jump/which-func hides /Applications/Emacs24.app/Contents/Resources/lisp/progmodes/which-func
/Users/steve/.emacs.d/site-lisp/rinari/util/ruby-mode hides /Applications/Emacs24.app/Contents/Resources/lisp/progmodes/ruby-mode
~/.emacs.d/site-lisp/org-mode/lisp/org hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org
~/.emacs.d/site-lisp/org-mode/lisp/org-xoxo hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-xoxo
~/.emacs.d/site-lisp/org-mode/lisp/org-wl hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-wl
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~/.emacs.d/site-lisp/org-mode/lisp/org-timer hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-timer
~/.emacs.d/site-lisp/org-mode/lisp/org-taskjuggler hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-taskjuggler
~/.emacs.d/site-lisp/org-mode/lisp/org-table hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-table
~/.emacs.d/site-lisp/org-mode/lisp/org-src hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-src
~/.emacs.d/site-lisp/org-mode/lisp/org-rmail hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-rmail
~/.emacs.d/site-lisp/org-mode/lisp/org-remember hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-remember
~/.emacs.d/site-lisp/org-mode/lisp/org-publish hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-publish
~/.emacs.d/site-lisp/org-mode/lisp/org-protocol hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-protocol
~/.emacs.d/site-lisp/org-mode/lisp/org-plot hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-plot
~/.emacs.d/site-lisp/org-mode/lisp/org-mouse hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mouse
~/.emacs.d/site-lisp/org-mode/lisp/org-mobile hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mobile
~/.emacs.d/site-lisp/org-mode/lisp/org-mks hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mks
~/.emacs.d/site-lisp/org-mode/lisp/org-mhe hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mhe
~/.emacs.d/site-lisp/org-mode/lisp/org-mew hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mew
~/.emacs.d/site-lisp/org-mode/lisp/org-macs hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-macs
~/.emacs.d/site-lisp/org-mode/lisp/org-mac-message hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-mac-message
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~/.emacs.d/site-lisp/org-mode/lisp/org-irc hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-irc
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~/.emacs.d/site-lisp/org-mode/lisp/org-info hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-info
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~/.emacs.d/site-lisp/org-mode/lisp/org-id hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-id
~/.emacs.d/site-lisp/org-mode/lisp/org-icalendar hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-icalendar
~/.emacs.d/site-lisp/org-mode/lisp/org-html hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-html
~/.emacs.d/site-lisp/org-mode/lisp/org-habit hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-habit
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~/.emacs.d/site-lisp/org-mode/lisp/org-footnote hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-footnote
~/.emacs.d/site-lisp/org-mode/lisp/org-feed hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-feed
~/.emacs.d/site-lisp/org-mode/lisp/org-faces hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-faces
~/.emacs.d/site-lisp/org-mode/lisp/org-exp hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-exp
~/.emacs.d/site-lisp/org-mode/lisp/org-exp-blocks hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-exp-blocks
~/.emacs.d/site-lisp/org-mode/lisp/org-entities hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-entities
~/.emacs.d/site-lisp/org-mode/lisp/org-docview hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-docview
~/.emacs.d/site-lisp/org-mode/lisp/org-docbook hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-docbook
~/.emacs.d/site-lisp/org-mode/lisp/org-datetree hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-datetree
~/.emacs.d/site-lisp/org-mode/lisp/org-ctags hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-ctags
~/.emacs.d/site-lisp/org-mode/lisp/org-crypt hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-crypt
~/.emacs.d/site-lisp/org-mode/lisp/org-compat hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-compat
~/.emacs.d/site-lisp/org-mode/lisp/org-colview hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-colview
~/.emacs.d/site-lisp/org-mode/lisp/org-clock hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-clock
~/.emacs.d/site-lisp/org-mode/lisp/org-capture hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-capture
~/.emacs.d/site-lisp/org-mode/lisp/org-bibtex hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-bibtex
~/.emacs.d/site-lisp/org-mode/lisp/org-beamer hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-beamer
~/.emacs.d/site-lisp/org-mode/lisp/org-bbdb hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-bbdb
~/.emacs.d/site-lisp/org-mode/lisp/org-attach hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-attach
~/.emacs.d/site-lisp/org-mode/lisp/org-ascii hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-ascii
~/.emacs.d/site-lisp/org-mode/lisp/org-archive hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-archive
~/.emacs.d/site-lisp/org-mode/lisp/org-agenda hides /Applications/Emacs24.app/Contents/Resources/lisp/org/org-agenda
~/.emacs.d/site-lisp/org-mode/lisp/ob hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob
~/.emacs.d/site-lisp/org-mode/lisp/ob-tangle hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-tangle
~/.emacs.d/site-lisp/org-mode/lisp/ob-table hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-table
~/.emacs.d/site-lisp/org-mode/lisp/ob-sqlite hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-sqlite
~/.emacs.d/site-lisp/org-mode/lisp/ob-sql hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-sql
~/.emacs.d/site-lisp/org-mode/lisp/ob-sh hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-sh
~/.emacs.d/site-lisp/org-mode/lisp/ob-screen hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-screen
~/.emacs.d/site-lisp/org-mode/lisp/ob-sass hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-sass
~/.emacs.d/site-lisp/org-mode/lisp/ob-ruby hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-ruby
~/.emacs.d/site-lisp/org-mode/lisp/ob-ref hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-ref
~/.emacs.d/site-lisp/org-mode/lisp/ob-R hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-R
~/.emacs.d/site-lisp/org-mode/lisp/ob-python hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-python
~/.emacs.d/site-lisp/org-mode/lisp/ob-perl hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-perl
~/.emacs.d/site-lisp/org-mode/lisp/ob-octave hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-octave
~/.emacs.d/site-lisp/org-mode/lisp/ob-ocaml hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-ocaml
~/.emacs.d/site-lisp/org-mode/lisp/ob-mscgen hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-mscgen
~/.emacs.d/site-lisp/org-mode/lisp/ob-matlab hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-matlab
~/.emacs.d/site-lisp/org-mode/lisp/ob-lob hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-lob
~/.emacs.d/site-lisp/org-mode/lisp/ob-latex hides /Applications/Emacs24.app/Contents/Resources/lisp/org/ob-latex
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format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process ns multi-tty emacs)

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Óscar Fuentes]

This problem also affects eshell:

cat foo | wc

hangs. As pointed out on the magit bug tracker, the problem was
introduced by this commit:

http://repo.or.cz/w/emacs.git/commitdiff/ee1b6e21aa2b831499659b7f58ec94b95016cec7

2010-06-01  Stefan Monnier  <monnier@iro.umontreal.ca>

       * sysdep.c (child_setup_tty): Move the non-canonical initialization to
       the HAVE_TERMIO where it belongs (bug#6149).

Reverting it fixes magit and eshell.

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Jan Djärv]

I enabled ICANON.  If there is a long line problem (i.e. a too long line to 
send_process may only send a partial line), please write a bug report for it 
with a way to reproduce it.  That way we can fix it.  I have not seen any 
problem or been able to reproduce the long line problem.

	Jan D.

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Óscar Fuentes]

Jan Djärv <jan.h.d@swipnet.se> writes:

> I enabled ICANON.  If there is a long line problem (i.e. a too long
> line to send_process may only send a partial line), please write a bug
> report for it with a way to reproduce it.  That way we can fix it.  I
> have not seen any problem or been able to reproduce the long line
> problem.

So the example command line on the attachment of bug#6149 does not
reproduce the problem?

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Jan Djärv]

Óscar Fuentes skrev 2010-08-02 16.37:
> Jan Djärv<jan.h.d@swipnet.se>  writes:
>
>> I enabled ICANON.  If there is a long line problem (i.e. a too long
>> line to send_process may only send a partial line), please write a bug
>> report for it with a way to reproduce it.  That way we can fix it.  I
>> have not seen any problem or been able to reproduce the long line
>> problem.
>
> So the example command line on the attachment of bug#6149 does not
> reproduce the problem?

No:

% echo ... | wc

        1     154    4881


	Jan D.

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Wolfgang Jenkner]

Jan Djärv <jan.h.d@swipnet.se> writes:

> I enabled ICANON.  If there is a long line problem (i.e. a too long
> line to send_process may only send a partial line), please write a bug
> report for it with a way to reproduce it.  That way we can fix it.  I
> have not seen any problem or been able to reproduce the long line
> problem.

FWIW, such a problem does exist in the wild.

The UIM emacs bridge (see [1]) sometimes sends long lines of about 20k
of ASCII characters to the uim-el-helper-agent subprocess.

Now, on FreeBSD 8-STABLE the maximum total size of a tty (or pty) input
queue is 1920 bytes, cf. tty_watermarks() in [2] and the discussion in
[3].  For Linux, judging from a superficial glance at tty_buffer_alloc()
in [4], the bound seems to be a more comfortable 65536 bytes.

For a self-contained example of what happens on breaking this bound,
evaluate the following form (adjust 1923 to taste) and observe that the
process output buffer contains only ASCII BEL (\C-g) characters, which
is (modulo bogus references to MAX_INPUT and MAX_CANON) what termios(4)
documents (search for IMAXBEL), i.e., the pseudo-terminal rings :-)

(let* ((buf (generate-new-buffer "cat-out"))
       (proc (start-process "cat" buf "cat")))
  (process-send-string proc (make-string 1923 ?x))
  (process-send-string proc "\n")
  (pop-to-buffer buf))

Of course, if line discipline features are not needed, a pipe can be
used as a work-around (and I intend to submit a patch in this sense to
the UIM developers or else to the FreeBSD port maintainer, which is one
reason why I wanted to have this issue documented here).

[1] http://code.google.com/p/uim/wiki/UIM_EL

[2] http://svn.freebsd.org/viewvc/base/stable/8/sys/kern/tty.c?view=markup

[3] http://lists.freebsd.org/pipermail/freebsd-stable/2009-October/052318.html

[3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/tty/tty_buffer.c;hb=HEAD

bug#6771: 24.0.50; Child process input isn't closed by process-send-eof; hangs indefinitely

[Štěpán Němec]

Wolfgang Jenkner <wjenkner@inode.at> writes:

> Jan Djärv <jan.h.d@swipnet.se> writes:
>
>> I enabled ICANON.  If there is a long line problem (i.e. a too long
>> line to send_process may only send a partial line), please write a bug
>> report for it with a way to reproduce it.  That way we can fix it.  I
>> have not seen any problem or been able to reproduce the long line
>> problem.
>
> FWIW, such a problem does exist in the wild.
>
> The UIM emacs bridge (see [1]) sometimes sends long lines of about 20k
> of ASCII characters to the uim-el-helper-agent subprocess.
>
> Now, on FreeBSD 8-STABLE the maximum total size of a tty (or pty) input
> queue is 1920 bytes, cf. tty_watermarks() in [2] and the discussion in
> [3].  For Linux, judging from a superficial glance at tty_buffer_alloc()
> in [4], the bound seems to be a more comfortable 65536 bytes.
>
> For a self-contained example of what happens on breaking this bound,
> evaluate the following form (adjust 1923 to taste) and observe that the
> process output buffer contains only ASCII BEL (\C-g) characters, which
> is (modulo bogus references to MAX_INPUT and MAX_CANON) what termios(4)
> documents (search for IMAXBEL), i.e., the pseudo-terminal rings :-)
>
> (let* ((buf (generate-new-buffer "cat-out"))
>        (proc (start-process "cat" buf "cat")))
>   (process-send-string proc (make-string 1923 ?x))
>   (process-send-string proc "\n")
>   (pop-to-buffer buf))
>
> Of course, if line discipline features are not needed, a pipe can be
> used as a work-around (and I intend to submit a patch in this sense to
> the UIM developers or else to the FreeBSD port maintainer, which is one
> reason why I wanted to have this issue documented here).

Although it would certainly be nice if this limitation disappeared,
using pipes instead is not necessarily a work-around -- it might simply
be the better solution for what you are doing, for other reasons as
well. As the Elisp manual puts it (info "(elisp)Asynchronous Processes"):

 -- Variable: process-connection-type
     This variable controls the type of device used to communicate with
     asynchronous subprocesses.  If it is non-`nil', then PTYs are
     used, when available.  Otherwise, pipes are used.

     PTYs are usually preferable for processes visible to the user, as
     in Shell mode, because they allow job control (`C-c', `C-z', etc.)
     to work between the process and its children, whereas pipes do
     not.  For subprocesses used for internal purposes by programs, it
     is often better to use a pipe, because they are more efficient.  In
     addition, the total number of PTYs is limited on many systems and
     it is good not to waste them.


  Štěpán