Re: undo in loaddefs.el buffer

[Jan D.]

Luc Teirlinck wrote:


> If, for instance, a timer is involved that runs once every five
> seconds, or even more frequently, then, after the quit, the timer will
> run again, make the undo entry even larger without adding an undo
> boundary and ask the question again.  And again, until something
> creates an undo boundary.  I do not _know_ whether something like this
> is happening in the situations described above, but until I committed
> a patch yesterday evening, the described behavior was exactly what would
> happen (with up to a five second delay) if you auto-reverted the
> Buffer Menu every five seconds.
>
> The popup menu could be explained by any intervening mouse click.

There is no timer, and there is no mouse click.  Just C-g, no mouse 
movement, or anything else.

Richard Stallman wrote:

>    For the original case (quitting out of the undo question), that would be 
>    an improvement as you could continue to hit Ctrl-g until all questions 
>    are gone :-).  It is a strange case.  I have to hit Ctrl-g three times 
>    for the yes-or-no question in the minibuffer to be canceled, but then a 
>    yes-or-no dialog pops up.
>
> I don't follow.  If you type C-g, that should quit the command that is
> asking the question, so it won't produce any more undo info and it
> won't ask any more questions.
>
> If something other than that happens for you, why does it happen?
> Is it a bug?

Here is what I found.

The first time the question to discard is asked, it is asked by kill-region:


#0  Fyes_or_no_p (prompt=141235155) at fns.c:3279
#1  0x081c238e in Ffuncall (nargs=2, args=0xbfffe150) at eval.c:2775
#2  0x081f6065 in Fbyte_code (bytestr=137004643, vector=137004684,
   maxdepth=40) at bytecode.c:686
#3  0x081c2b84 in funcall_lambda (fun=137004612, nargs=1,
   arg_vector=0xbfffe374) at eval.c:2962
#4  0x081c25ab in Ffuncall (nargs=2, args=0xbfffe370) at eval.c:2823
#5  0x081c1fc5 in call1 (fn=138840169, arg1=61097120) at eval.c:2569
#6  0x081a3a86 in truncate_undo_list (b=0x83931e0) at undo.c:379
#7  0x081a829e in Fgarbage_collect () at alloc.c:4687
#8  0x081f5cbc in Fbyte_code (bytestr=137012651, vector=137012724,
   maxdepth=40) at bytecode.c:523
#9  0x081c15fa in Feval (form=137012637) at eval.c:2136
#10 0x081c00b7 in Fcondition_case (args=140356805) at eval.c:1332
#11 0x081f6814 in Fbyte_code (bytestr=137012587, vector=137012612,
   maxdepth=24) at bytecode.c:864
#12 0x081c2b84 in funcall_lambda (fun=137012524, nargs=2,
   arg_vector=0xbfffe9e4) at eval.c:2962
#13 0x081c25ab in Ffuncall (nargs=3, args=0xbfffe9e0) at eval.c:2823
#14 0x081be2e3 in Fcall_interactively (function=138212161,
   record_flag=137916553, keys=137975548) at callint.c:877
#15 0x08155340 in Fcommand_execute (cmd=138212161, record_flag=137916553,
   keys=137916553, special=137916553) at keyboard.c:9712
#16 0x081486e2 in command_loop_1 () at keyboard.c:1785
#17 0x081c01ca in internal_condition_case (bfun=0x81472f1 <command_loop_1>,
   handlers=137979985, hfun=0x8146e2e <cmd_error>) at eval.c:1385
#18 0x08147173 in command_loop_2 () at keyboard.c:1312
#19 0x081bfca9 in internal_catch (tag=137973201,
   func=0x8147150 <command_loop_2>, arg=137916553) at eval.c:1144
#20 0x08147129 in command_loop () at keyboard.c:1291
#21 0x08146bb0 in recursive_edit_1 () at keyboard.c:984
#22 0x08146cf5 in Frecursive_edit () at keyboard.c:1045
#23 0x0814565b in main (argc=2, argv=0xbffff3d4) at emacs.c:1763
(gdb) xbacktrace
"yes-or-no-p"
"undo-outer-limit-truncate"
"byte-code"
"kill-region"
"call-interactively"

But when I hit C-g, Emacs does redisplay, and that in turn invokes a GC, 
which asks the question again:

#0  Fyes_or_no_p (prompt=141235011) at fns.c:3279
#1  0x081c238e in Ffuncall (nargs=2, args=0xbfffdd30) at eval.c:2775
#2  0x081f6065 in Fbyte_code (bytestr=137004643, vector=137004684,
   maxdepth=40) at bytecode.c:686
#3  0x081c2b84 in funcall_lambda (fun=137004612, nargs=1,
   arg_vector=0xbfffdf54) at eval.c:2962
#4  0x081c25ab in Ffuncall (nargs=2, args=0xbfffdf50) at eval.c:2823
#5  0x081c1fc5 in call1 (fn=138840169, arg1=61097120) at eval.c:2569
#6  0x081a3a86 in truncate_undo_list (b=0x83931e0) at undo.c:379
#7  0x081a829e in Fgarbage_collect () at alloc.c:4687
#8  0x081c2119 in Ffuncall (nargs=2, args=0xbfffe0e0) at eval.c:2715
#9  0x081c1fc5 in call1 (fn=138013281, arg1=137972113) at eval.c:2569
#10 0x08149427 in safe_run_hooks_1 (hook=-1073749696) at keyboard.c:2037
#11 0x081c01ca in internal_condition_case (bfun=0x814940b 
<safe_run_hooks_1>,
   handlers=137916601, hfun=0x8149429 <safe_run_hooks_error>) at 
eval.c:1385
#12 0x081494c1 in safe_run_hooks (hook=137972113) at keyboard.c:2065
#13 0x080a57df in update_menu_bar (f=0x85a4e00, save_match_data=0)
   at xdisp.c:8305
#14 0x080a557f in prepare_menu_bars () at xdisp.c:8204
#15 0x080a826f in redisplay_internal (preserve_echo_area=0) at xdisp.c:9881
#16 0x080a73f4 in redisplay () at xdisp.c:9482
#17 0x08149cb9 in read_char (commandflag=1, nmaps=2, maps=0xbfffea90,
   prev_event=137916553, used_mouse_menu=0xbfffeb8c) at keyboard.c:2537
#18 0x081533f3 in read_key_sequence (keybuf=0xbfffecf0, bufsize=30,
   prompt=137916553, dont_downcase_last=0, can_return_switch_frame=1,
   fix_current_buffer=1) at keyboard.c:8818
#19 0x08147690 in command_loop_1 () at keyboard.c:1531
#20 0x081c01ca in internal_condition_case (bfun=0x81472f1 <command_loop_1>,
   handlers=137979985, hfun=0x8146e2e <cmd_error>) at eval.c:1385
#21 0x08147173 in command_loop_2 () at keyboard.c:1312
#22 0x081bfca9 in internal_catch (tag=137973201,
   func=0x8147150 <command_loop_2>, arg=137916553) at eval.c:1144
#23 0x08147129 in command_loop () at keyboard.c:1291
#24 0x08146bb0 in recursive_edit_1 () at keyboard.c:984
#25 0x08146cf5 in Frecursive_edit () at keyboard.c:1045
#26 0x0814565b in main (argc=2, argv=0xbffff3d4) at emacs.c:1763
(gdb) xbacktrace
"yes-or-no-p"
"undo-outer-limit-truncate"

(gdb) l alloc.c:4687
4682        /* If a buffer's undo list is Qt, that means that undo is
4683           turned off in that buffer.  Calling truncate_undo_list on
4684           Qt tends to return NULL, which effectively turns undo 
back on.
4685           So don't call truncate_undo_list if undo_list is Qt.  */
4686        if (! EQ (nextb->undo_list, Qt))
4687          truncate_undo_list (nextb);
4688   
4689        /* Shrink buffer gaps, but skip indirect and dead buffers.  */
4690        if (nextb->base_buffer == 0 && !NILP (nextb->name))
4691          {
(gdb)


And from that point on every C-g leads to a redisplay and a GC, and the 
same place in alloc.c again, until I answer Yes or No on the question.

As for the dialog popping up, I can only assume that read_key_sequence 
gets interrupted by the C-g after it has set last_nonmenu_event to Qnil, 
but before it has set it to the event.  This is however just 
speculation, I haven't been able to actually catch that in the 
debugger.  Running inside the debugger has the strange side effect of 
never popping up a dialog, so there might be some timing involved.

   Jan D.