Re: [PATCH] Unconditional quit on SIGUSR2

[joakim]

Daniel Colascione <address@hidden> writes:

> On 3/29/11 10:55 AM, Daniel Colascione wrote:
>>
>> Below is another version of the patch.  I've changed the code so that we
>> instead inspect a new debug-on-special-event variable, which by default
>> is the symbol sigusr2.  This way, we can extend the mechanism and use
>> another kind of special event for platforms that lack signals.
>> 
>
> Does anyone have any strong objections to merging this patch?

I haven't used your patch but I often feel the need to be able to
interrupt an Emacs that does not respond for some reason. If your patch
gives me another tool to try in those cases, I would be very interested
in having it applied to trunk.

Would it be possible also to have some "run level 1" functionality? That
is, when the signal is sent, Emacs disables timers, font-lock etc...

>
> === modified file 'doc/emacs/trouble.texi'
> --- doc/emacs/trouble.texi    2011-01-25 04:08:28 +0000
> +++ doc/emacs/trouble.texi    2011-03-29 17:47:26 +0000
> @@ -812,6 +812,14 @@
>  This backtrace is useful for debugging such long loops, so if you can
>  produce it, copy it into the bug report.
>  
> address@hidden debug-on-special-event
> +If the normal quit process is ineffective, you can try sending Emacs
> +the special event given in @code{debug-on-special-event}, which by
> +default corresponds to SIGUSR2.  When Emacs receives this event, it
> +stops what it's doing, sets @code{debug-on-quit} to @code{t}, and
> +tries to break into the debugger in a variety of ways.  This process
> +happens even in places where quitting is normally not allowed.
> +
>  @item
>  Check whether any programs you have loaded into the Lisp world,
>  including your @file{.emacs} file, set any variables that may affect the
>
> === modified file 'doc/lispref/debugging.texi'
> --- doc/lispref/debugging.texi        2011-01-25 04:08:28 +0000
> +++ doc/lispref/debugging.texi        2011-03-29 17:46:44 +0000
> @@ -185,6 +185,20 @@
>  when you quit.  @xref{Quitting}.
>  @end defopt
>  
> address@hidden debug-on-special-event
> +When this variable contains a symbol matching one of the special
> +events in @code{special-event-map} (@pxref{Active Keymaps}) and Emacs
> +receives the corresponding event, Emacs will break into the debugger
> +instead of processing the event normally, setting @code{debug-on-quit}
> +to @code{t} as a side effect.  This feature is useful for terminating
> +infinite loops in places where quits would normally be ignored, such
> +as in code that runs during redisplay.
> +
> +Currently, the only events Emacs recognizes as valid values for
> address@hidden are @code{sigusr1} and @code{sigusr2}.
> +
> address@hidden defopt
> +
>  @node Function Debugging
>  @subsection Entering the Debugger on a Function Call
>  @cindex function call debugging
>
> === modified file 'lisp/cus-start.el'
> --- lisp/cus-start.el 2011-03-27 10:55:07 +0000
> +++ lisp/cus-start.el 2011-03-29 17:36:51 +0000
> @@ -259,6 +259,11 @@
>            (suggest-key-bindings keyboard (choice (const :tag "off" nil)
>                                                   (integer :tag "time" 2)
>                                                   (other :tag "on")))
> +             (debug-on-special-event debug
> +                         (choice (const :tag "None" nil)
> +                                    (const :tag "When sent SIGUSR1" sigusr1)
> +                                    (const :tag "When sent SIGUSR2" sigusr2))
> +                            "24.1")
>  
>  ;; This is not good news because it will use the wrong
>  ;; version-specific directories when you upgrade.  We need
>
> === modified file 'src/keyboard.c'
> --- src/keyboard.c    2011-03-27 02:27:11 +0000
> +++ src/keyboard.c    2011-03-29 17:29:47 +0000
> @@ -7165,12 +7165,33 @@
>  {
>    int old_errno = errno;
>    struct user_signal_info *p;
> +  const char* special_event_name = NULL;
>  
>    SIGNAL_THREAD_CHECK (sig);
> -
> +  
> +  if (SYMBOLP (Vdebug_on_special_event) &&
> +      STRINGP (XSYMBOL (Vdebug_on_special_event)->xname))
> +    {
> +      special_event_name =
> +        SSDATA (XSYMBOL (Vdebug_on_special_event)->xname);
> +    }
> +  
>    for (p = user_signals; p; p = p->next)
>      if (p->sig == sig)
>        {
> +        if (special_event_name &&
> +            strcmp (special_event_name, p->name) == 0)
> +          {
> +            /* Enter the debugger in many ways.  */
> +            debug_on_next_call = 1;
> +            debug_on_quit = 1;
> +            Vquit_flag = Qt;
> +            Vinhibit_quit = Qnil;
> +
> +            /* Eat the event.  */
> +            break;
> +          }
> +        
>       p->npending++;
>  #ifdef SIGIO
>       if (interrupt_input)
> @@ -12178,6 +12199,17 @@
>  `deactivate-mark' call uses this to set the window selection.  */);
>    Vsaved_region_selection = Qnil;
>  
> +  DEFVAR_LISP ("debug-on-special-event",
> +               Vdebug_on_special_event,
> +               doc: /* Enter debugger on this special event.
> +When Emacs receives the special event specifed by this variable,
> +it will try to break into the debugger as soon as possible instead of
> +processing the event normally through `special-event-map'.
> +
> +Currently, the only meaningful values for this
> +variable are `sigusr1' and `sigusr2'.  */);
> +  Vdebug_on_special_event = intern_c_string ("sigusr2");
> +
>    /* Create the initial keyboard. */
>    initial_kboard = (KBOARD *) xmalloc (sizeof (KBOARD));
>    init_kboard (initial_kboard);
>
> === modified file 'src/lisp.h'
> --- src/lisp.h        2011-03-27 02:27:11 +0000
> +++ src/lisp.h        2011-03-28 13:06:41 +0000
> @@ -2814,7 +2814,7 @@
>  
>  /* Defined in eval.c */
>  extern Lisp_Object Qautoload, Qexit, Qinteractive, Qcommandp, Qdefun, Qmacro;
> -extern Lisp_Object Qinhibit_quit;
> +extern Lisp_Object Qinhibit_quit, Qdebug;
>  extern Lisp_Object Vautoload_queue;
>  extern Lisp_Object Vsignaling_function;
>  extern int handling_signal;
>

-- 
Joakim Verona