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Re: Concurrency via isolated process/thread

From: Ihor Radchenko
Subject: Re: Concurrency via isolated process/thread
Date: Fri, 07 Jul 2023 12:30:16 +0000

Eli Zaretskii <eliz@gnu.org> writes:

>> So, my efforts did reduce the time spent in allocate_vectorlike.
>> Note, however, that these two datapoints differ more than just by how
>> memory is allocated.
>> But 5% CPU time spend allocating memory is not insignificant.
> Once again, it isn't necessarily memory allocation per se.  For
> example, it could be find_suspicious_object_in_range, called from
> allocate_vectorlike.

I did not have ENABLE_CHECKING in this benchmark.
It is just ./configure --with-native-compilation
So, find_suspicious_object_in_range should not run at all.

>> Sure. Though my argument was less about how long Emacs spends allocating
>> memory and more about how frequently a typical Elisp code requests such
>> allocations. I have a gut feeling that even if taking short time,
>> frequent interrupts may create intermittent typing delays.
> I very much doubt these interrupts are because Emacs waits for memory
> allocation.

I guess we can be optimistic. And if not, maybe need to have multiple heaps.

>> If a thread is working with a temporary buffer and locks it, that
>> buffer has almost 0 chance to be accessed by another thread.
> But "working on a buffer" requires access and modification of many
> global structures.  Just walk the code in set-buffer and its
> subroutines, and you will see that.

I was only able to identify the following:


AFAIU, current_buffer might be made thread-local and
last_known_column_point can be made buffer-local.

interrupt_input_blocked is more tricky. But it is just one global state
variable. Surely we can find a solution to make it work with multiple threads.

>> Same with variables - even if some global variable needs to be locked,
>> it is unlikely that it will need to be accessed by another thread.
> I think you misunderstand the frequency of such collisions.
> case-fold-search comes to mind.

How so? What is the problem with a buffer-local variable that is rarely
set directly (other than by major modes)? let-binding is common, but it
is not a problem.

Ihor Radchenko // yantar92,
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>

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