Opinion needed: multiprocessing usage

[Augie Fackler]

(+indygreg)

> On Nov 11, 2019, at 03:04, Pierre-Yves David <pierre-yves.david at ens-lyon.org> wrote:
> 
> Hi everyone,
> 
> I am looking into introducing parallelism into `hg debugupgraderepo`. I already have a very useful prototype that precompute in // copies information when converting to side-data storage. That prototype use multiprocessing because it is part of the stdlib and work quite well for this usecase.
> 
> However, I know we refrained to use multiprocessing in the past. I know the import and boostrap cost was to heavy for things like `hg update`. However, I am not sure if there are other reason to rule out the multiprocessing module in the `hg debugupgraderepo` case.

I have basically only ever heard bad things about multiprocessing, especially on Windows which is the platform where you'd expect it to be the most useful (since there's no fork()). I think Greg has more details in his head.

That said, I guess feel free to experiment, in the knowledge that it probably isn't significantly better than our extant worker system?

> 
> Cheers,
> 
> -- 
> Pierre-Yves David
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