Re: MPS: User GC customizations

[Eli Zaretskii <eliz@gnu.org>]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: Ihor Radchenko <yantar92@posteo.net>,  Eli Zaretskii <eliz@gnu.org>,
>   emacs-devel@gnu.org,  eller.helmut@gmail.com
> Date: Thu, 04 Jul 2024 18:07:42 +0200
> 
> Pip Cet <pipcet@protonmail.com> writes:
> 
> > I think we can just set flags for "called MPS" and "in a scan
> > function" and look at them in the SIGPROF handler to distinguish the
> > four cases?
> 
> Not sure. What if MPS calls these in its own thread? I guess that
> wouldn't be so interesting for Ihor.

AFAIU, on GNU/Linux signals are delivered to the main thread,

> Darwin is a kind of Mach descendant, and as such it uses Mach exceptions
> for hardware faults. Among those is EXC_BAD_ACCESS which one gets for
> protection faults. Exceptions are handled by installing a "port"
> which runs in its own thread and which the OS invokes when the exception
> occurs.
> 
> Exception handling is "synchronous", which I think means the OS suspends
> the thread which caused the exception, invokes the port for doing what
> it wants, and when done let's the original thread continue, if the port
> wants that.

That's very similar to what happens on Windows, at least on this high
level of description.