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bug#9216: Signal handling and pthreads

From: Stefan Monnier
Subject: bug#9216: Signal handling and pthreads
Date: Mon, 01 Aug 2011 13:44:09 -0400

In syssignal.h we have:

   #if defined (HAVE_GTK_AND_PTHREAD) || defined (HAVE_NS)
   #include <pthread.h>
   /* If defined, asynchronous signals delivered to a non-main thread are
      forwarded to the main thread.  */

But that is not right: the test should bot be for HAVE_NS and HAVE_GTK,
but just for using pthreads.  There are more ways to get
pthreads involved.  E.g. I just got the following assertion failure:

   #0  abort () at emacs.c:381
   #1  0x08373ba2 in die (
       msg=0x860ae8c "assertion failed: handling_signal == 0", 
       file=0x8603867 "keyboard.c", line=7183) at alloc.c:6232
   #2  0x082be485 in input_available_signal (signo=29) at keyboard.c:7183
   #3  <signal handler called>
   #4  0xb7fe2424 in __kernel_vsyscall ()
   #5  0xb73b5f86 in poll () from /lib/i386-linux-gnu/i686/cmov/libc.so.6
   #6  0xb7890f5b in g_poll () from /lib/libglib-2.0.so.0
   #7  0xb788096f in ?? () from /lib/libglib-2.0.so.0
   #8  0xb78810f3 in g_main_loop_run () from /lib/libglib-2.0.so.0
   #9  0xb64396f4 in ?? () from /usr/lib/gio/modules/libdconfsettings.so
   #10 0xb78a9b6f in ?? () from /lib/libglib-2.0.so.0
   #11 0xb77dec39 in start_thread ()
      from /lib/i386-linux-gnu/i686/cmov/libpthread.so.0
   #12 0xb73c396e in clone () from /lib/i386-linux-gnu/i686/cmov/libc.so.6

Where the "handling_signal == 0" check is one I added to
input_available_signal right after the SIGNAL_THREAD_CHECK.  This is
with a Lucid build: pthreads gets involved because of
libdconfsettings, apparently.

IOW we should also set FORWARD_SIGNAL_TO_MAIN_THREAD when using
libdconfsettings (and maybe some more).  Tho a better fix might be to
better set up our signal handlers so we don't need this
SIGNAL_THREAD_CHECK hack which seems unreliable (it drops signals on
the floor when delivered to the wrong thread, which would seem to mean
the main thread may fail to be told about pending input to be processed).


In GNU Emacs (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2011-08-01 on ceviche
Windowing system distributor `The X.Org Foundation', version 11.0.11002000
configured using `configure  'CFLAGS=-Wall -Wno-pointer-sign 
-g -O1 -I/usr/include/GNUstep' '--enable-maintainer-mode' 

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: fr_CH.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: InactiveMinibuffer

Minor modes in effect:
  electric-pair-mode: t
  electric-indent-mode: t
  url-handler-mode: t
  global-reveal-mode: t
  reveal-mode: t
  auto-insert-mode: t
  savehist-mode: t
  minibuffer-electric-default-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<switch-frame> <select-window> <select-window> C-x 
5 0 M-x r e - e m - b u <tab> <return>

Recent messages:
Loading ~/src/elisp/bbdb/lisp/bbdb-autoloads...done
Loading /home/monnier/src/elisp/ProofGeneral/generic/proof-site.el 
Warning: set-coding-priority is obsolete!
Warning: interactive-p is obsolete!
Loading /home/monnier/src/elisp/sml-mode/sml-mode-startup.el (source)...done
Loading /home/monnier/etc/emacs/X11.el (source)...done
Loading /home/monnier/etc/emacs/custom.el (source)...done
Ispell-kill: nil american
Starting new Ispell process [american] ...
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

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