Re: MPS: weak hash tables

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 06 Jul 2024 05:58:19 +0000
> From: Pip Cet <pipcet@protonmail.com>
> Cc: Helmut Eller <eller.helmut@gmail.com>, Eli Zaretskii <eliz@gnu.org>, Emacs Devel <emacs-devel@gnu.org>
> 
> > > What I'm doing right now is alternating usleep(10000) and
> > > igc_collect() in a secondary thread. That crashes somewhat
> > > reproducibly in interactive sessions.
> > 
> > Could you please make that available in some form?
> 
> Sure. I was thinking about cleaning it up (usleep is non-standard) and committing it behind a stress-test option, actually.
> 
> Right now it's dying because specpdl is a union type and GC might hit while the main thread leaves it in a partially-initialized state. I vaguely recall turning it into a struct for that reason on another branch years ago...
> 
> Pip
> 
> diff --git a/src/igc.c b/src/igc.c
> index f154a040a0e..be2b9fb719e 100644
> --- a/src/igc.c
> +++ b/src/igc.c
> @@ -4820,6 +4820,16 @@ igc_busy_p (void)
>    return mps_arena_busy (global_igc->arena);
>  }
>  
> +static void *
> +igc_thread_fun (void *addr)
> +{
> +  while (true)
> +    {
> +      usleep (5000);
> +      igc_collect ();
> +    }
> +}
> +
>  /***********************************************************************
>  				  Init
>   ***********************************************************************/
> @@ -4830,6 +4840,8 @@ init_igc (void)
>    mps_lib_assert_fail_install (igc_assert_fail);
>    global_igc = make_igc ();
>    add_main_thread ();
> +  pthread_t thr;
> +  pthread_create (&thr, NULL, igc_thread_fun, global_igc);
>    set_state (IGC_STATE_USABLE_PARKED);
>  }

Thanks, but why is this important or interesting?  We are not going to
add native threads to Emacs.

Also, AFAIU, MPS docs says to register each thread with it, and your
code doesn't, AFAICT.