Re: Some experience with the igc branch

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

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> New day, new beliefs :-). Today, when I read my question again, I'd
> actually be surprised if a signal handler could allocate Lisp objects
> because I wouldn't be able to explain how that works with alloc.c which
> isn't reentrant. Not even Fcons is reentrant when I look at it now.
>
> Correct, or am I overlooking something? Could others please check? If
> it's right, things get a lot easier.

I agree.  But Eli said something about wanting to run Lisp from a signal
handler, which would change that.  I was trying to explain why we don't
want to do that.

> Maybe allocation of Lisp objects on the stack remains as some sort of
> problem (AUTO_CONS etc)? I don't see how though, ATM.

Stack objects are always optional, so if there is code that attempts to
avoid alloc.c by using those, it's broken.

My current patch makes it so the main thread never takes the arena lock,
ever.  Performance isn't quite the same as scratch/igc: for some reason
I don't understand, it's slightly better.  Still needs cleanup,
de-pthreading, and we probably don't need to use atomic types
everywhere.

Pip