Re: save-excursion and multi-thread?

[Eli Zaretskii]

> From: Qiantan Hong <qhong@mit.edu>
> CC: "emacs-devel@gnu.org" <emacs-devel@gnu.org>
> Date: Sun, 26 Sep 2021 19:21:38 +0000
> 
> >> I see. Can I fake that with indirect-buffer?
> > 
> > For moving point, I think you can.  But if you change the text, you
> > will see the changes in the other threads as well.
> That’s intended. 
> I simply want point to behave like a proper global variable

But point is not a variable.  It's a property of a buffer, and all you
have is a (read-only) accessor to that property.

> and save-excursion to behave like a proper let-binding.

You can always use save-excursion in the other thread, no?

> In that sense I don’t want point to be thread local, 
> I want save-excursion to be thread local, which I think
> is the only sensible concurrent semantics for save-excursion.
> Only in that way save-excursion really serves its intended purpose
> — to have “local” excursion that doesn’t affect global state
> outside the code it surrounds.

That's one way of looking at save-excursion.  Another way is to look
at it as a means for a thread to protect its own position of point
from changes by other threads.  So from that POV, it's the other
thread which needs to use save-excursion.

> Does that convince you?

Convince me to do what? redesign and reimplement Lisp threads in
Emacs with very different design goals?