GNU bug report logs - #13290
24.2.91; [PATCH] Comint can stall emacs with non-trivial input senders

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Vitalie Spinu <spinuvit <at> gmail.com>
Subject: bug#13290: closed (Re: bug#13290: 24.2.91; [PATCH] Comint can
 stall emacs with non-trivial input senders)
Date: Mon, 07 Jan 2013 01:08:02 +0000

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Your bug report

#13290: 24.2.91; [PATCH] Comint can stall emacs with non-trivial input senders

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 13290 <at> debbugs.gnu.org.

-- 
13290: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=13290
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Glenn Morris <rgm <at> gnu.org>
To: 13290-done <at> debbugs.gnu.org
Subject: Re: bug#13290: 24.2.91;
	[PATCH] Comint can stall emacs with non-trivial input senders
Date: Sun, 06 Jan 2013 20:07:06 -0500

Version: 24.2.92

OK; applied.

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From: Vitalie Spinu <spinuvit <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2.91; [PATCH] Comint can stall emacs with non-trivial input senders
Date: Thu, 27 Dec 2012 22:49:01 +0100

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Hi, 

Comint can stall emacs while waiting for subproces output. I attach a
trivial patch.

Here is a short explanation. First comint calls comint-input-sender 

╭──────── #1842 ─ /home/vitoshka/TVC/emacs/lisp/comint.el ──
│         (let ((comint-input-sender-no-newline no-newline))
│           (funcall comint-input-sender proc input))
╰──────── #1843 ─

Then, if process echoes, comint first waits for process output:

╭──────── #1850 ─ /home/vitoshka/TVC/emacs/lisp/comint.el ──
│             (while (and (accept-process-output proc)
│                         (> (+ comint-last-input-end echo-len)
│                            (point-max))
╰──────── #1852 ─

The problem is that, occasionally, comint-input-sender might be a
non-trivial function and could take care of process output itself. Thus,
accept-process-output will wait for nonexistent output, and stall
emacs. The patch just reverts the order in the (and ...) above.

    Thanks, 
    Vitalie

[0001-Avoid-hanging-emacs-by-complex-comint-input-senders.patch (text/x-diff, inline)]

From d3c2753a571688370a4bc8fa2254679d9c23b74a Mon Sep 17 00:00:00 2001
From: Vitalie Spinu <spinuvit <at> gmail.com>
Date: Thu, 27 Dec 2012 21:46:38 +0100
Subject: [PATCH] Avoid hanging emacs by complex comint input senders.

Revert the order of echo-len check and accept-process-output to avoid stalling
Emacs when there is no process output left.
---
 lisp/ChangeLog |    6 ++++++
 lisp/comint.el |    4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 5f4853d..cc94b0d 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,9 @@
+2012-12-27  Vitalie Spinu  <spinuvit <at> gmail.com>
+
+	* comint.el (comint-send-input): revert the order of echo-len
+	check and accept-process-output to avoid hanging Emacs when there
+	is no process output left.
+
 2012-12-27  Michael Albinus  <michael.albinus <at> gmx.de>
 
 	* net/tramp.el (tramp-handle-file-accessible-directory-p): New defun.
diff --git a/lisp/comint.el b/lisp/comint.el
index f3450e3..6477f00 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -1847,9 +1847,9 @@ Similarly for Soar, Scheme, etc."
           (let ((echo-len (- comint-last-input-end
                              comint-last-input-start)))
             ;; Wait for all input to be echoed:
-            (while (and (accept-process-output proc)
-                        (> (+ comint-last-input-end echo-len)
+            (while (and (> (+ comint-last-input-end echo-len)
                            (point-max))
+                        (accept-process-output proc)
                         (zerop
                          (compare-buffer-substrings
                           nil comint-last-input-start
-- 
1.7.10.4

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In GNU Emacs 24.2.91.1 (i686-pc-linux-gnu, GTK+ Version 2.24.13)
 of 2012-12-25 on vitoshka-home
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:	Ubuntu 12.10

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

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