Re: igc, macOS avoiding signals

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Helmut Eller <eller.helmut@gmail.com>
>> Cc: Pip Cet <pipcet@protonmail.com>,  Eli Zaretskii <eliz@gnu.org>,
>>   spd@toadstyle.org,  emacs-devel@gnu.org
>> Date: Mon, 30 Dec 2024 17:57:02 +0100
>> 
>> On Mon, Dec 30 2024, Gerd Möllmann wrote:
>> 
>> > Bool (LockIsHeld)(Lock lock)
>> > {
>> >   AVERT(Lock, lock);
>> >   if (pthread_mutex_trylock(&lock->mut) == 0) {
>> >     Bool claimed = lock->claims > 0;
>> >     int res = pthread_mutex_unlock(&lock->mut);
>> >     AVER(res == 0);
>> >     return claimed;
>> >   }
>> >   return TRUE;
>> > }
>> >
>> > There might be a small window after pthread_mutex_trylock and being back
>> > in the signal handler. Can anything happen in this window?
>> >
>> > If no other Emacs threads are running, and the Emacs thread is in the
>> > signal handler, we can trust the "false" from the mps_arena_busy.
>> 
>> Theoretically, a signal handler could interrupt the Emacs thread and
>> lock the mutex without unlocking it.  That would be a very unusual
>> signal handler.  I hope no other surprises happen in signal handlers.
>
> We should keep our signal handlers very simple and safe, that's true.
> It is not very hard, and much of that work was already done, when we
> stopped running complex stuff in SIGIO handler etc.

So, to summarize, everyone agrees with Helmut?