Re: igc, macOS avoiding signals

[Helmut Eller]

On Mon, Dec 30 2024, Pip Cet wrote:

>> Theoretically, a signal handler could interrupt the Emacs thread and
>> lock the mutex without unlocking it.
>
> I don't think that's a problem.  Here's why:
>
> We'd have to call the POSIX police.  I believe it's a conscious POSIX
> decision not to allow hand-over of locks from one thread/signal handler
> (those can't even call _trylock) to another;

Do you mean, it is not allowed to call pthread_mutex_trylock in a signal
handler?

[...]
> But anyway, POSIX prohibits it, glibc on GNU/Linux doesn't support it,
> I'm not aware of any other systems making that useful, certainly not for
> Emacs.
>
>> That would be a very unusual signal handler.  I hope no other
>> surprises happen in signal handlers.
>
> longjmp-based green threads?  (MPS currently assumes a simple linear
> stack, gcc can produce split-stack code, getting that combination to
> work would be good; I can dig up the patch for enabling it for the old
> GC).

I think MPS would require a special thread module that can handle green
threads.  Probably nothing we have to worry about.

Helmut