Re: SIGTRAP in kill emulation on Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Alain Schneble <a.s@realize.ch>
> CC: <emacs-devel@gnu.org>
> Date: Fri, 26 Aug 2016 10:58:58 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Sending SIGTRAP to a process -- whether it's an unrelated, child or the
> >> calling Emacs process itself -- does not seem to have any effect as long
> >> as no debugger is attached to the receiving process.
> >
> > Do you see the same with the debugbreak program you've built earlier?
> > If not, then that program does something that your patch doesn't.
> 
> Yes, debugbreak and the proposed implementation behave identically.

Then I guess that's a limitation we will have to live with.  It
doesn't sound like a grave one to me: after all, what exactly SIGTRAP
does when no debugger is attached is not very important, since that is
not the primary use case for that signal, AFAIU.  If a Lisp program
wants to kill the process, it doesn't need to use SIGTRAP.

> >> But with all processes I tried, none of them was ever terminated.
> >
> > That's a pity; on GNU/Linux the target program does terminate.  If
> > there's nothing that can be done, we will just have to document this
> > quirk, at least for many/most programs Emacs users will meet on their
> > systems.
> 
> Yes, and on GNU/Linux I observed that it prints a backtrace prior to
> termination.

That depends on ulimit and suchlikes, I think: on a GNU/Linux system I
tried that, the program was simply dumped to the shell prompt without
printing anything.

> But that's kind of irrelevant here I guess.  Where would be the best
> place to document this quirk (c, signal-process, info manual)?

In the Info manual, I think.

> FWIW, there is probably something we could do about it -- query if the
> process in question is attached to a debugger.  If not, we could
> terminate it.

That's for the application to decide, IMO.  Signal delivery is too
low-level to replace one signal with another one.