Simon Willison’s Weblog

gh-116167: Allow disabling the GIL with PYTHON_GIL=0 or -X gil=0. Merged into python:main 14 hours ago. Looks like the first phase of Sam Gross’s phenomenal effort to provide a GIL free Python (here via an explicit opt-in) will ship in Python 3.13. # 12th March 2024, 5:40 am

A Steering Council notice about PEP 703 (Making the Global Interpreter Lock Optional in CPython) (via) Huge news concerning the nogil research fork of Python: “It’s clear that the overall sentiment is positive, both for the general idea and for PEP 703 specifically. The Steering Council is also largely positive on both. We intend to accept PEP 703, although we’re still working on the acceptance details.” # 29th July 2023, 9:23 pm

The Python Language Summit 2023: Making the Global Interpreter Lock Optional. Extremely informative update covering Sam Gross’s python-nogil proposal from this year’s language summit at PyCon.

Sam has been working hard on his fork for the past year, and now has it rebased for Python 3.12. If his PEP is accepted it could end up as an optional compile-time build in time for Python 3.13.

“The plan for nogil remains that it would be enabled via a compile-time flag, named --disable-gil. Third-party C extensions would need to provide separate wheels for GIL-disabled Python.” # 31st May 2023, 12:04 am

Real Multithreading is Coming to Python—Learn How You Can Use It Now (via) Martin Heinz provides a detailed tutorial on trying out the new Per-Interpreter GIL feature that’s landing in Python 3.12, which allows Python code to run concurrently in multiple threads by spawning separate sub-interpreters, each with their own dedicated GIL.

It’s not an easy feature to play with yet! First you need to compile Python yourself, and then use APIs that are generally only available to C code (but should hopefully become available to Python code itself in Python 3.13).

Martin’s workaround for this is ingenious: it turns out the Python test.support package provides utility functions to help write tests against interpreters, and Martin shows how to abuse this module to launch, run and cleanup interpreters using regular Python code.

He also demonstrates test.support.interpreters.create_channel(), which can be used to create channels with receiver and sender ends, somewhat similar to Go. # 15th May 2023, 7:42 pm

Testing Datasette parallel SQL queries in the nogil/python fork. As part of my ongoing research into whether Datasette can be sped up by running SQL queries in parallel I’ve been growing increasingly suspicious that the GIL is holding me back. I know the sqlite3 module releases the GIL and was hoping that would give me parallel queries, but it looks like there’s still a ton of work going on in Python GIL land creating Python objects representing the results of the query.

Sam Gross has been working on a nogil fork of Python and I decided to give it a go. It’s published as a Docker image and it turns out trying it out really did just take a few commands... and it produced the desired results, my parallel code started beating my serial code where previously the two had produced effectively the same performance numbers.

I’m pretty stunned by this. I had no idea how far along the nogil fork was. It’s amazing to see it in action. # 29th April 2022, 5:45 am

[history] When I tried this in 1996 (via) “I removed the GIL back in 1996 from Python 1.4...” is the start of a fascinating (supportive) comment by Greg Stein on the promising nogil Python fork that Sam Gross has been putting together. Greg provides some historical context that I’d never heard before, relating to an embedded Python for Microsoft IIS. # 21st February 2022, 10:43 pm

The GIL and its effects on Python multithreading (via) Victor Skvortsov presents the most in-depth explanation of the Python Global Interpreter Lock I’ve seen anywhere. I learned a ton from reading this. # 29th September 2021, 5:23 pm

jessenoller.com—python magazine. Jesse Noller has been sharing his articles originally published in Python Magazine. Topics include SSH programming with Paramiko, context managers and the with statement and an excellent explanation of Python’s threading support and the global interpreter lock. # 5th February 2009, 11:10 pm

What’s New in Python 2.6. The new multiprocessing package looks pretty useful, especially as it provides a way to work around Python’s GIL. # 1st September 2008, 9:03 pm