Re: Emacs design and architecture. How about copy-on-write?

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

> That avoids garbled values where part of a value is from one thread,
> the other part from another thread.  But it does nothing to protect
> the threads other than the one which changed the value from the
> "surprise" of having stuff change under its feet.  Which is the main
> problem to solve, since Emacs code is written under the assumption
> that a variable in the global state doesn't change while some code
> runs that doesn't change that variable.  That is why access to at
> least some things will have to be serialized -- to allow threads that
> access some part of the global state some level of control on what can
> and cannot change while they are doing their job.

My solution (which I've put into practice in redisplay) is to save those
values before sensitive code is executed, and to refer to those saved
values within said code.

But right now I'm stymied by the representation of buffer-local
variables (or rather the lack thereof in a multiprocessing Emacs), so I
plan to give this subject a break for a week or two and revisit it
later.