[Python-3000] Kill GIL?

Paul Prescod paul at prescod.net
Mon Sep 18 10:19:40 CEST 2006

On 9/17/06, Ivan Krstić <krstic at solarsail.hcs.harvard.edu> wrote:

> At present, the Python approach to multi-processing sounds a bit like
> "let's stick our collective hands in the sand and pretend there's no
> problem". In particular, one oft-parroted argument says that it's not
> worth changing or optimizing the language for the few people who can
> afford SMP hardware. In the meantime, dual-core laptops are becoming the
> standard, with Intel predicting quad-core will become mainstream in the
> next few years, and the number of server orders for single-core, UP
> machines is plummeting.

I agree with you Ivan.

Even if I won't contribute code or even a design to the solution (because it
isn't an area of expertise and I'm still working on encodings stuff) I think
that there would be value in saying: "There's a big problem here and we
intend to fix it in Python 3000."

When you state baldly that something is a problem you encourage the
community to experiement with and debate solutions. But I have been in the
audience at Python conferences where the majority opinion was that Python
had no problem around multi-processor apps because you could just roll your
own IPC on top of processes.

If you have to roll your own, that's a problem. If you have to select
between five solutions with really subtle tradeoffs, that's a problem too.

Ivan: why don't you write a PEP about this?

> * Bite the bullet; write and support a stdlib SHM primitive that works
> wherever possible, and simply doesn't work on completely broken
> platforms (I understand Windows falls into this category). Utilize it in
> a lightweight fork-and-coordinate wrapper provided in the stdlib.

Such a low-level approach will not fly. Not just because of Windows but also
because of Jython and IronPython. But maybe I misunderstand it in general.
Python does not really have an abstraction as low-level "memory" and I don't
see why we would want to add it.

* Introduce microthreads, declare that Python endorses Erlang's
> no-sharing approach to concurrency, and incorporate something like
> candygram into the stdlib.
> * Introduce a fork-and-coordinate wrapper in the stdlib, and declare
> that we're simply not going to support the use case that requires
> sharing (as opposed to merely passing) objects between processes.

I'm confused on a few levels.

 1. "No sharing" seems to be a feature of both of these options, but the
wording you use to describe it is very different.

 2. You're conflating API and implementation in a manner that is unclear to
me. Why are microthreads important to the Erlang model and what would the
API for fork-and-coordinate look like?

Since you are fired up about this now, would you consider writing a PEP at
least outlining the problem persuasively and championing one of the
(feasible) options? This issue has been discussed for more than a decade and
the artifacts of previous discussions can be quite hard to find.

 Paul Prescod
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