Hang while scrolling buffer with PNG images

[Ralf Angeli]

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

The problem is actually happening with preview-latex (current CVS
version), a package for generating inline previews of LaTeX code.  The
previews are normally PNG images.

The package comes with an example file called `circ.tex'.  I can
reproduce a hang of Emacs with circ.tex by doing a `C-c C-p C-d y',
waiting for the compilation to finish and hitting the down arrow on
the keyboard until I reach the line of the file which says "$y$-Wert
dar.Jetzt formen wir ...".  In this state the rendered equation below
the line is only partly visible.  With the cursor on the rendered $y$
hitting the down key again produces a hang.  One can still move the
scroll bar but there will be no reaction in the buffer.  The same is
true for hitting any of the cursor keys.  In this state Emacs is
hogging about 99% of the CPU resources.

In the reply to a bug report filed against preview-latex, David
Kastrup, the author of preview-latex, assumed that the problem is with
the PNG loading code of Emacs.

While Emacs was hanging I attached to the process with gdb and
generated the following backtrace.  I hope it is helpful:

,----[ (gdb) bt ]
| #0  0x080bad36 in face_at_buffer_position (w=0x8623cd0, pos=2499,
|     region_beg=-1, region_end=-1, endptr=0xbfffddb8, limit=-1073750764,
|     mouse=0) at xfaces.c:7313
| #1  0x08062d37 in handle_face_prop (it=0xbfffdee0) at xdisp.c:2776
| #2  0x080627d8 in handle_stop (it=0xbfffdee0) at xdisp.c:2502
| #3  0x0806690f in next_element_from_buffer (it=0xbfffdee0) at xdisp.c:5314
| #4  0x08065cd8 in get_next_display_element (it=0xbfffdee0) at xdisp.c:4666
| #5  0x080762b4 in display_line (it=0xbfffdee0) at xdisp.c:14300
| #6  0x080725b8 in try_window (window=1214397648, pos=
|       {charpos = -1073750304, bytepos = 1055}) at xdisp.c:12034
| #7  0x0806eebf in try_scrolling (window=1214397648, just_this_one_p=1,
|     scroll_conservatively=0, scroll_step=1, temp_scroll_step=0,
|     last_line_misfit=1055) at xdisp.c:10937
| #8  0x08071dfb in redisplay_window (window=1214397648, just_this_one_p=1)
|     at xdisp.c:11743
| #9  0x0806e5a5 in redisplay_window_1 (window=0) at xdisp.c:10464
| #10 0x08143cf4 in internal_condition_case_1 (
|     bfun=0x806e570 <redisplay_window_1>, arg=1214397648, handlers=1479568512,
|     hfun=0x806e510 <redisplay_window_error>) at eval.c:1374
| #11 0x0806d723 in redisplay_internal (preserve_echo_area=0) at xdisp.c:10090
| #12 0x0806ca32 in redisplay () at xdisp.c:9447
| #13 0x080e7695 in read_char (commandflag=1, nmaps=5, maps=0xbfffee5c,
|     prev_event=405781212, used_mouse_menu=0xbfffeea8) at keyboard.c:2495
| #14 0x080ee177 in read_key_sequence (keybuf=0xbfffefd0, bufsize=30,
|     prompt=405781212, dont_downcase_last=0, can_return_switch_frame=1,
|     fix_current_buffer=1) at keyboard.c:8825
| #15 0x080e4482 in command_loop_1 () at keyboard.c:1504
| #16 0x08143bee in internal_condition_case (bfun=0x80e42e0 <command_loop_1>,
|     handlers=405892308, hfun=0x80e3e50 <cmd_error>) at eval.c:1333
| #17 0x080e418d in command_loop_2 () at keyboard.c:1292
| #18 0x0814374b in internal_catch (tag=0, func=0x80e4160 <command_loop_2>,
|     arg=405781212) at eval.c:1094
| #19 0x080e413c in command_loop () at keyboard.c:1271
| #20 0x080e3be4 in recursive_edit_1 () at keyboard.c:987
| #21 0x080e3d11 in Frecursive_edit () at keyboard.c:1043
| #22 0x080e2432 in main (argc=1, argv=0xbffff654) at emacs.c:1666
`----

Unfortunately I don't have a testcase without using preview-latex.
But maybe someone can reproduce this anyway.

Cheers,
Ralf


In GNU Emacs 21.3.50.5 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2003-09-03 on iwi71
Important settings:
  value of $LC_ALL: en_US
  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: en_US
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Recent input:
M-x r e p o r t - e <tab> <return>

Recent messages:
Loading time...done
Loading byte-opt...done
Loading font-lock...
Source file `/usr/local/share/emacs/21.3.50/lisp/emacs-lisp/syntax.el' newer 
than byte-compiled file
Loading font-lock...done
Loading cl-macs...done
Loading kmacro...done
Loading two-column...done
For information about the GNU Project and its goals, type C-h C-p.
Loading emacsbug...done