Re: 23.0.60; Emacs should survive a lost X connection

[Dan Nicolaescu <dann@ics.uci.edu>]

Richard Stallman <rms@gnu.org> writes:

  > 		* eval.c (internal_condition_case_2, internal_condition_case_1)
  > 		(internal_condition_case): Reenable abort if x_catching_errors ()
  > 		to see if that really happens and why.
  > 
  > 
  >     Richard, now you have part of the answer: if the X11 connection is lost
  >     emacs crashes after your patch. It works fine after undoing the patch.
  > 
  > Interesting.  Can you send me a backtrace for that crash?

Sure: 

#0  abort () at /tmp/emacs/src/emacs.c:432
#1  0x081627ad in internal_condition_case_2 (bfun=0x81655b0 <Frun_hook_with_args>, nargs=2, args=0xbfbcc6c4, handlers=137640185, 
    hfun=0x805cb30 <delete_frame_handler>) at /tmp/emacs/src/eval.c:1573
#2  0x0805d451 in Fdelete_frame (frame=146544260, force=137640185) at /tmp/emacs/src/frame.c:1412
#3  0x080d4cf5 in x_connection_closed (dpy=0x87f6b88, error_message=<value optimized out>)
    at /tmp/emacs/src/xterm.c:8054
#4  0x080d4dbb in x_io_error_quitter (display=0x87f6b88) at /tmp/emacs/src/xterm.c:8202
#5  0x00206fc2 in _XIOError () from /usr/lib/libX11.so.6
#6  0x0020dbb9 in ?? () from /usr/lib/libX11.so.6
#7  0x0020df9f in _XEventsQueued () from /usr/lib/libX11.so.6
#8  0x001f76d2 in XPending () from /usr/lib/libX11.so.6
#9  0x080d876e in XTread_socket (terminal=0x8853f48, expected=1, hold_quit=0xbfbccfa4)
    at /tmp/emacs/src/xterm.c:7366
#10 0x081019df in read_avail_input (expected=1) at /tmp/emacs/src/keyboard.c:7110
#11 0x08101b0a in handle_async_input () at /tmp/emacs/src/keyboard.c:7340
#12 0x08101cd1 in input_available_signal (signo=29) at /tmp/emacs/src/keyboard.c:7382
#13 <signal handler called>
#14 0x00110402 in __kernel_vsyscall ()
#15 0x007eb5bd in ___newselect_nocancel () from /lib/libc.so.6
#16 0x08190f05 in select_wrapper (n=1, rfd=0x0, wfd=0xbfbcd528, xfd=0x0, tmo=0xbfbcd658)
    at /tmp/emacs/src/process.c:4240
#17 0x08194110 in wait_reading_process_output (time_limit=30, microsecs=0, read_kbd=-1, do_display=1, wait_for_cell=137640137, 
    wait_proc=0x0, just_wait_proc=0) at /tmp/emacs/src/process.c:4610
#18 0x08052220 in sit_for (timeout=240, reading=1, do_display=1) at /tmp/emacs/src/dispnew.c:6608
#19 0x08106dbd in read_char (commandflag=1, nmaps=2, maps=0xbfbcd930, prev_event=137640137, used_mouse_menu=0xbfbcd9d8, 
    end_time=0x0) at /tmp/emacs/src/keyboard.c:2969
#20 0x08108b0a in read_key_sequence (keybuf=0xbfbcda74, bufsize=30, prompt=137640137, dont_downcase_last=0, 
    can_return_switch_frame=1, fix_current_buffer=1) at /tmp/emacs/src/keyboard.c:9460
#21 0x0810a9a3 in command_loop_1 () at /tmp/emacs/src/keyboard.c:1655
#22 0x08162ab2 in internal_condition_case (bfun=0x810a800 <command_loop_1>, handlers=137684369, hfun=0x8104f70 <cmd_error>)
    at /tmp/emacs/src/eval.c:1496
#23 0x081043e3 in command_loop_2 () at /tmp/emacs/src/keyboard.c:1370
#24 0x08162b6a in internal_catch (tag=137679217, func=0x81043c0 <command_loop_2>, arg=137640137)
    at /tmp/emacs/src/eval.c:1230
#25 0x08104dd7 in command_loop () at /tmp/emacs/src/keyboard.c:1349
#26 0x0810513a in recursive_edit_1 () at /tmp/emacs/src/keyboard.c:958
#27 0x08105271 in Frecursive_edit () at /tmp/emacs/src/keyboard.c:1020
#28 0x080faa97 in main (argc=5, argv=0xbfbce174) at /tmp/emacs/src/emacs.c:1793

(This is from doing:
emacs -Q -nw -f server-start 
in a terminal,
then on another display:
emacsclient -c -d $DISPLAY
then kill X11)

  >     (Undoing this patch also solves another issue discussed recently: emacs
  >     crashes after using xkill on an emacsclient frame).
  > 
  > I'd like to see a backtrace for that case too.

Here it is:

#0  abort () at /tmp/emacs/src/emacs.c:432
#1  0x081627ad in internal_condition_case_2 (bfun=0x81655b0 <Frun_hook_with_args>, nargs=2, args=0xbfaf8de4, handlers=137640185, 
    hfun=0x805cb30 <delete_frame_handler>) at /tmp/emacs/src/eval.c:1573
#2  0x0805d451 in Fdelete_frame (frame=146544260, force=137640185) at /tmp/emacs/src/frame.c:1412
#3  0x080d4cf5 in x_connection_closed (dpy=0x87f6b88, error_message=<value optimized out>)
    at /tmp/emacs/src/xterm.c:8054
#4  0x080d4dbb in x_io_error_quitter (display=0x87f6b88) at /tmp/emacs/src/xterm.c:8202
#5  0x00206fc2 in _XIOError () from /usr/lib/libX11.so.6
#6  0x0020dbb9 in ?? () from /usr/lib/libX11.so.6
#7  0x0020df9f in _XEventsQueued () from /usr/lib/libX11.so.6
#8  0x001f76d2 in XPending () from /usr/lib/libX11.so.6
#9  0x080d876e in XTread_socket (terminal=0x8853f48, expected=1, hold_quit=0xbfaf96c4)
    at /tmp/emacs/src/xterm.c:7366
#10 0x081019df in read_avail_input (expected=1) at /tmp/emacs/src/keyboard.c:7110
#11 0x08101b0a in handle_async_input () at /tmp/emacs/src/keyboard.c:7340
#12 0x08101cd1 in input_available_signal (signo=29) at /tmp/emacs/src/keyboard.c:7382
#13 <signal handler called>
#14 0x00110402 in __kernel_vsyscall ()
#15 0x007eb5bd in ___newselect_nocancel () from /lib/libc.so.6
#16 0x08190f05 in select_wrapper (n=1, rfd=0x0, wfd=0xbfaf9c48, xfd=0x0, tmo=0xbfaf9d78)
    at /tmp/emacs/src/process.c:4240
#17 0x08194110 in wait_reading_process_output (time_limit=30, microsecs=0, read_kbd=-1, do_display=1, wait_for_cell=137640137, 
    wait_proc=0x0, just_wait_proc=0) at /tmp/emacs/src/process.c:4610
#18 0x08052220 in sit_for (timeout=240, reading=1, do_display=1) at /tmp/emacs/src/dispnew.c:6608
#19 0x08106dbd in read_char (commandflag=1, nmaps=2, maps=0xbfafa050, prev_event=137640137, used_mouse_menu=0xbfafa0f8, 
    end_time=0x0) at /tmp/emacs/src/keyboard.c:2969
#20 0x08108b0a in read_key_sequence (keybuf=0xbfafa194, bufsize=30, prompt=137640137, dont_downcase_last=0, 
    can_return_switch_frame=1, fix_current_buffer=1) at /tmp/emacs/src/keyboard.c:9460
#21 0x0810a9a3 in command_loop_1 () at /tmp/emacs/src/keyboard.c:1655
#22 0x08162ab2 in internal_condition_case (bfun=0x810a800 <command_loop_1>, handlers=137684369, hfun=0x8104f70 <cmd_error>)
    at /tmp/emacs/src/eval.c:1496
#23 0x081043e3 in command_loop_2 () at /tmp/emacs/src/keyboard.c:1370
#24 0x08162b6a in internal_catch (tag=137679217, func=0x81043c0 <command_loop_2>, arg=137640137)
    at /tmp/emacs/src/eval.c:1230
#25 0x08104dd7 in command_loop () at /tmp/emacs/src/keyboard.c:1349
#26 0x0810513a in recursive_edit_1 () at /tmp/emacs/src/keyboard.c:958
#27 0x08105271 in Frecursive_edit () at /tmp/emacs/src/keyboard.c:1020
#28 0x080faa97 in main (argc=5, argv=0xbfafa894) at /tmp/emacs/src/emacs.c:1793

The above is from:
emacs -Q -nw -f server-start
from another xterm:
emacsclient -c -d :0

from yet another xterm:

xkill

and click on the X11 frame created by emacsclient


The abort is because of this code in internal_condition_case_2:

#if HAVE_X_WINDOWS
  if (x_catching_errors ())
    abort ();
#endif

x_connection_closed does an:

  x_catch_errors (dpy);

but the condition that x_catching_errors looks for is different. (I have no idea whether this is relevant or not).