Re: igc, macOS avoiding signals

[Helmut Eller]

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.

Helmut