GNU bug report logs - #57197
28.1.90; Can pure side-effect-free functions use multiple CPUs in Elisp?

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From: Akib Azmain Turja <akib <at> disroot.org>
To: yantar92 <at> gmail.com, 57197 <at> debbugs.gnu.org
Subject: bug#57197: 28.1.90; Can pure side-effect-free functions use multiple CPUs in Elisp?
Date: Mon, 15 Aug 2022 11:57:31 +0600

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> Hi,
> 
> The known blocker of Elisp support of multi-threading is shared Elisp
> machine state. Handling competing access to global Elisp variables is
> tricky. However, it is not the case for pure side-effect-free functions.
> 
> Consider the following code:
> 
> (let (long-list-of-cons)
>   (dotimes (i 100000)
>     (push (cons i (1+ i)) long-list-of-cons))
>   (mapcar #'car long-list-of-cons))
> 
> The last mapcar looks like a good candidate to run on multiple CPUs.
> I imagine that instead of applying #'car sequentially, Elisp can split
> the list in chunks and run them independently on multiple CPUs. This
> operation is still blocking and thus will not create issues with shared
> access. At the same time such mapcar call will finish much faster.
> 
> Would something like this be feasible to implement in Elisp?
> 
> -- 
> Ihor Radchenko,
> Org mode contributor,
> Learn more about Org mode at https://orgmode.org/.
> Support Org development at https://liberapay.com/org-mode,
> or support my work at https://liberapay.com/yantar92
>

I think the problem is the interpreter itself, which is not thread-safe.
This looks like a feature request, I think emacs-devel is good for that.

-- 
Akib Azmain Turja

Find me on Mastodon at @akib <at> hostux.social.

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