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From: Philipp
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Subject: Re: Is automatic yield support feasible for threads?
Date: Thu, 11 Nov 2021 19:11:10 +0100
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Archived-At:
> Am 10.11.2021 um 08:46 schrieb ndame :
>=20
> On Tuesday, November 9th, 2021 at 3:53 PM, Philipp =
wrote:
>>=20
>> I don't think it's feasible. Emacs Lisp code typically relies heavily =
on mutating global state (think buffer contents, the buffer list, =
`point', dynamic variables, ...), and normally doesn't put such state =
mutations into properly synchronized critical sections. Yielding from =
such unprotected critical sections would result in very subtle bugs =
(`point' randomly moving around, corruption of internal data structures, =
buffers vanishing surprisingly, ...).
>=20
> I don't think threads should be used for UI manipulation, that should =
be left for the main thread. Threads are more useful for longer running =
calculations, computations and those should have no problem if they work =
on local data.
There are two problems with that approach:
1. Emacs doesn't clearly separate UI work from non-UI work. For =
example, buffers are primarily a UI feature, but are also widely used =
for string manipulation unrelated to any UI action, and such uses are =
typically considered implementation details.
2. There are many coding patterns involving global state mutations that =
are unrelated to UI actions, e.g., caching the result of an expensive =
computation.
>=20
> But you are right if someone uses a thread for UI changes then there =
can be problems. My idea is about an _optional_ automatic yielding for =
threads, so it still could be useful for those threads which are self =
contained.
Only trivial thread bodies are guaranteed to be self-contained. You'd =
need to audit every single function that the thread body calls whether =
it performs any unsynchronized global state mutations, which is =
infeasible since such state mutations are generally considered =
implementation details, and functions typically don't document them.