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

From: Po Lu
Subject: Re: Emacs design and architecture. How about copy-on-write?
Date: Wed, 20 Sep 2023 21:35:49 +0800
User-agent: Gnus/5.13 (Gnus v5.13)

Po Lu <luangruo@yahoo.com> writes:

> Ihor Radchenko <yantar92@posteo.net> writes:
>> Does it mean that each threads contains a copy of the whole `globals'? I
>> think I proposed this in the linked thread and it was objected as
>> something taking a lot of memory.
> It incorporates one pointer for each field within globals itself.  AFAIU
> that was the initial impetus for introducing struct emacs_globals in the
> first place.
>> IMHO, copy-of-write would be better here - only store the thread-local
>> values that are actually altered by the thread.
> Of course only specbound values will be saved within each thread's
> state, but each thread must maintain a pointer to the field that is
> actually holding the value of the forwarded variables.
>> Indeed, a simple #define will not be enough then, but we would not waste
>> memory copying the values that will never be changed anyway.
> On my machine, struct emacs_globals is 7490 bytes, just short of 7 KiB.

Correction: just over 7 KiB.

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