Re: Question about display engine

[Ergus <spacibba@aol.com>]

On Sun, Oct 13, 2019 at 07:06:18PM +0300, Eli Zaretskii wrote:
>> Date: Sun, 13 Oct 2019 17:40:52 +0200
>> From: Ergus <spacibba@aol.com>
>> Cc: rudalics@gmx.at, emacs-devel@gnu.org
>>
>> #0  0x000055cb1453ac98 in redisplay_windows (window=0x55cb15e3bfb5) at ../../src/xdisp.c:16126
>> #1  0x000055cb1453ac6d in redisplay_windows (window=0x55cb163ffc55) at ../../src/xdisp.c:16120
>> #2  0x000055cb1455b35d in redisplay_internal () at ../../src/xdisp.c:15596
>> #3  0x000055cb145fff3f in read_char (commandflag=1, map=0x55cb16838f93, prev_event=0x0, used_mouse_menu=0x7ffc1a89f4eb, end_time=0x0) at ../../src/keyboard.c:2473
>> #4  0x000055cb1460278a in read_key_sequence
>>     (keybuf=<optimized out>, prompt=0x0, dont_downcase_last=<optimized out>, can_return_switch_frame=true, fix_current_buffer=true, prevent_redisplay=<optimized out>)
>>     at ../../src/keyboard.c:9527
>> #5  0x000055cb14603e2c in command_loop_1 () at ../../src/lisp.h:1032
>> #6  0x000055cb1466af87 in internal_condition_case
>>     (bfun=bfun@entry=0x55cb14603c30 <command_loop_1>, handlers=handlers@entry=0x90, hfun=hfun@entry=0x55cb145fadc0 <cmd_error>) at ../../src/eval.c:1355
>> #7  0x000055cb145f5b94 in command_loop_2 (ignore=ignore@entry=0x0) at ../../src/lisp.h:1032
>> #8  0x000055cb1466aee1 in internal_catch (tag=tag@entry=0xd4a0, func=func@entry=0x55cb145f5b70 <command_loop_2>, arg=arg@entry=0x0) at ../../src/eval.c:1116
>> #9  0x000055cb145f5b3b in command_loop () at ../../src/lisp.h:1032
>> #10 0x000055cb145fa9d6 in recursive_edit_1 () at ../../src/keyboard.c:714
>> #11 0x000055cb145fad02 in Frecursive_edit () at ../../src/keyboard.c:786
>> #12 0x000055cb1451c957 in main (argc=18, argv=<optimized out>) at ../../src/emacs.c:2055
>>
>> After some other tests I just did; I found that:
>>
>> #0 seems to be the root of the loop. redisplay_windows never ends (inf
>>  loop) and I can't understand why. But at least this explains why in gui
>>  it works but not in tui, because there is the WINDOWP test.
>
>The WINDOWP test has nothing to do with GUI vs TTY, it tests whether
>w->contents is a window or a buffer.
>
>> What I can't understand is how the code can be in #1 that should always
>> filtered by the WINDOWP condition in tui right?
>
>No, see above.
>
>This function is a simple depth-first tree traversal of the window
>tree, starting from the root window of a frame.  Each leaf of the
>window tree has a buffer in its w->contents pointer, while
>intermediate nodes of the tree have windows in that pointer.
>
>> In any case the inf loop is there, but the recursions levels does not
>> grow... so after the first time it enters in #1, it goes in the other
>> branch if the if.
>
>If it goes to the other branch, it should descend the tree via the
>w->next pointer, and eventually get to a leaf node.
>
>Could it be that redisplay_window_0, or some function it calls,
>signals an error, which is caught by internal_condition_case_1?  What
>happens if you put a breakpoint in signal_or_quit, does it get called
>from redisplay_window or some other function called by
>redisplay_windows?

Yes, actually:

#0  0x00005597732a0380 in signal_or_quit (error_symbol=0x2cd0, data=0x559775ee2633, keyboard_quit=false) at ../../src/eval.c:1586
#1  0x000055977314c308 in Fsignal (error_symbol=<optimized out>, error_symbol@entry=0x2cd0, data=<optimized out>) at ../../src/eval.c:1568
#2  0x000055977314c4c9 in xsignal (data=<optimized out>, error_symbol=0x2cd0) at ../../src/lisp.h:4139
#3  0x000055977314c4c9 in xsignal2 (error_symbol=error_symbol@entry=0x2cd0, arg1=<optimized out>, arg2=<optimized out>) at ../../src/eval.c:1713
#4  0x000055977314b76e in args_out_of_range (a1=<optimized out>, a2=<optimized out>) at ../../src/lisp.h:1032
#5  0x000055977314e97b in validate_interval_range (object=0x559775cee0d5, begin=0x7fff35ec34b8, end=0x7fff35ec34b8, force=<optimized out>) at ../../src/textprop.c:158
#6  0x00005597732f4050 in Ftext_properties_at (position=<optimized out>, object=<optimized out>) at ../../src/textprop.c:572
#7  0x00005597732f40bc in Fget_text_property (position=<optimized out>, prop=0x5d30, object=<optimized out>) at ../../src/textprop.c:592
#8  0x00005597731f8eec in face_at_buffer_position
    (w=0x5597758e7620, pos=0, endptr=endptr@entry=0x7fff35ec3650, limit=100, mouse=mouse@entry=false, base_face_id=1, attr_filter=LFACE_EXTEND_INDEX)
    at ../../src/xfaces.c:6090
#9  0x000055977316ab25 in face_at_pos (it=0x7fff35ec3710, attr_filter=LFACE_EXTEND_INDEX) at ../../src/xdisp.c:4167
#10 0x000055977317083d in extend_face_to_end_of_line (it=0x7fff35ec3710) at ../../src/xdisp.c:21584
#11 0x0000559773185891 in display_mode_line (w=w@entry=0x5597758e7620, face_id=<optimized out>, format=0x7efd5d2d9ed3) at ../../src/xdisp.c:24990
#12 0x0000559773185afe in display_mode_lines (w=w@entry=0x5597758e7620) at ../../src/lisp.h:730
#13 0x000055977319ebbc in redisplay_window (window=0x5597758e7625, just_this_one_p=<optimized out>) at ../../src/xdisp.c:18803
#14 0x00005597731a327b in redisplay_window_0 (window=window@entry=0x5597758e7625) at ../../src/xdisp.c:16146
#15 0x000055977329f014 in internal_condition_case_1
    (bfun=bfun@entry=0x5597731a3250 <redisplay_window_0>, arg=arg@entry=0x5597758e7625, handlers=<optimized out>, hfun=hfun@entry=0x559773165800 <redisplay_window_error>) at ../../src/eval.c:1379
#16 0x000055977316ec98 in redisplay_windows (window=0x5597758e7625) at ../../src/xdisp.c:16126
#17 0x000055977316ec6d in redisplay_windows (window=0x5597758e7415) at ../../src/xdisp.c:16120
#18 0x000055977318f35d in redisplay_internal () at ../../src/xdisp.c:15596
#19 0x0000559773233f3f in read_char (commandflag=1, map=0x559775ee36d3, prev_event=0x0, used_mouse_menu=0x7fff35ec8cbb, end_time=0x0) at ../../src/keyboard.c:2473
#20 0x000055977323678a in read_key_sequence
    (keybuf=<optimized out>, prompt=0x0, dont_downcase_last=<optimized out>, can_return_switch_frame=true, fix_current_buffer=true, prevent_redisplay=<optimized out>)
    at ../../src/keyboard.c:9527
#21 0x0000559773237e2c in command_loop_1 () at ../../src/lisp.h:1032
#22 0x000055977329ef87 in internal_condition_case
    (bfun=bfun@entry=0x559773237c30 <command_loop_1>, handlers=handlers@entry=0x90, hfun=hfun@entry=0x55977322edc0 <cmd_error>) at ../../src/eval.c:1355
#23 0x0000559773229b94 in command_loop_2 (ignore=ignore@entry=0x0) at ../../src/lisp.h:1032
#24 0x000055977329eee1 in internal_catch (tag=tag@entry=0xd4a0, func=func@entry=0x559773229b70 <command_loop_2>, arg=arg@entry=0x0) at ../../src/eval.c:1116
#25 0x0000559773229b3b in command_loop () at ../../src/lisp.h:1032
#26 0x000055977322e9d6 in recursive_edit_1 () at ../../src/keyboard.c:714
#27 0x000055977322ed02 in Frecursive_edit () at ../../src/keyboard.c:786
#28 0x0000559773150957 in main (argc=18, argv=<optimized out>) at #../../src/emacs.c:2055

This makes more sense now.