Re: MPS: profiler

[Helmut Eller <eller.helmut@gmail.com>]

On Fri, Jun 21 2024, Gerd Möllmann wrote:

> I'm still not sure. What I'm trying to say is that we need to be sure
> that there are no windows left in which things can change. I'd be most
> comfortable ATM if the first thing the SIGPROF handler does is check
> is_busy and immediately returns, doing nothing.

Let's assume for moment that SIGPROF and SIGSEGV are handled in the same
thread.  Then either SIGPROF comes before SIGSEGV or after.

Case 1 (SEGPROF before SIGSEGV): here mps_arena_busy will return false
and will access the MPS-managed memory.  This is fine, because to MPS
this is no different than any other client code.

Case 2 (SEGSEGV before SIGPROF): here mps_arena_busy will return true
and we only increase a counter.  This is also fine.

Convinced this is safe and that we that have covered all cases?

Now for the harder situation where SIGPROF and SIGSEGV aren't handled in
the same thread.  Well, I would say that this doesn't happen in Emacs.
But maybe somebody can come up with example where it does.