Re: igc, macOS avoiding signals

[Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>]

"Eli Zaretskii" <eliz@gnu.org> writes:

>> From: Helmut Eller <eller.helmut@gmail.com>
>> Cc: Eli Zaretskii <eliz@gnu.org>,  pipcet@protonmail.com,
>>   spd@toadstyle.org,  emacs-devel@gnu.org
>> Date: Tue, 31 Dec 2024 08:34:42 +0100
>>
>> On Mon, Dec 30 2024, Gerd Möllmann wrote:
>>
>> > Eli Zaretskii <eliz@gnu.org> writes:
>> >
>> >>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> >>> Cc: Helmut Eller <eller.helmut@gmail.com>,  pipcet@protonmail.com,
>> >>>   spd@toadstyle.org,  emacs-devel@gnu.org
>> >>> Date: Mon, 30 Dec 2024 19:37:38 +0100
>> >>>
>> >>> So, to summarize, everyone agrees with Helmut?
>>
>> Except the POSIX police: it says that pthread_mutex_trylock isn't async
>> signal safe.  I suppose this also makes it's unsafe to use MPS's fault
>> handler in an async signal handler.  Bummer.  (Does the police take
>> bribes?)
>
> Doesn't MPS itself call it from a SIGSEGV handler?

Worse, it calls pthread_mutex_lock, IIUC.  This isn't POSIX but works
(on GNU/Linux, it works as long as you don't make the mutex recursive or
rely on deadlock detection.  IIRC MPS uses normal or error-checking
mutexes only and only uses deadlock detection to abort).

>> I wonder if the backtrace that we see in the signal handler is any
>> different from the backrace that we would see at the next safe point
>> (i.e. the next time maybe_quit is called).
>
> I think we cannot rely on that, because maybe_quit must be called by
> hand, it isn't magic.  We call it from various places in the
> interpreter, which could well be in some other place of a Lisp
> program.
>
> Once again, why not ask the MPS folks to give us a callback?  Or maybe
> we could try hacking MPS ourselves first, to see if that does the job,
> and ask them then?

I'm not sure what your suggestion is at this point, sorry.  You said in
another email not too long ago that you wanted to improve the current
code by special-casing "simple" signals; I agreed; now you appear to be
saying we should wait for an MPS modification.

Pip