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Re: Releasing the thread global_lock from the module API


From: Dmitry Gutov
Subject: Re: Releasing the thread global_lock from the module API
Date: Sat, 2 Mar 2024 17:35:26 +0200
User-agent: Mozilla Thunderbird

On 02/03/2024 07:57, tomas@tuxteam.de wrote:
On Sat, Mar 02, 2024 at 01:53:05AM +0200, Dmitry Gutov wrote:
On 01/03/2024 21:30, tomas@tuxteam.de wrote:
- Unrelated Lisp thread B is able to take the global lock and run Lisp code
    in parallel with module_work on thread A.
- On thread A, module_work finishes and returns to Lisp.
Why has thread A wait up to here? This is what's keeping your thread B
from playing, no?

I imagine thread A will want to continue its execution when the results of
the "Emacs-independent work" arrive.

In that case, I think your only choice would be to "pass the continuation":
in A, stash away whatever you need to continue, let A die, and when things
"come back", start a thread A' to pick up where A left.

Almost, except "suspend/yield" instead of "let A die".

And if the Lisp threads are backed by OS threads, such thread is waiting without purpose while "suspended" - Spencer's suggestion could put it to work in the meantime as well. Though the difference in performance might not be very significant, given our overhead in other places.

Said work might look like making a network request (as Spencer outlined),
getting a response, parsing the received JSON structure (not into Lisp
objects yet, just into the native data structures provided by the library),
and potentially filtering the parsed structure as well.

Then the lock is re-acquired (which will naturally involve some spinning
waiting for it), and the parsed data is converted into Lisp structures.

I'm always wary when people call for "threads" when they mean concurrency.

Yes, our Lisp threads are a bit unusual, terminology-wise.



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