Congrats on this impressive work Sam. I enjoyed the thorough write up of the design. There’s one aspect that I don’t quite understand. Maybe I missed the explanation. For example: ``` • Load the address of the item • Increment the reference count of the item, if it is non-zero (otherwise retry) • Return the address of the item (We typically acquire the per-collection mutex when retrying operations to avoid potential livelock issues.) ``` I’m unclear what is actually retried. You use this note throughout the document, so I think it would help to clarify exactly what is retried and why that solves the particular problem. I’m confused because, is it the refcount increment that’s retried or the entire sequence of steps (i.e. do you go back and reload the address of the item)? Is there some kind of waiting period before the retry? I would infer that if you’re retrying the refcount incrementing, it’s because you expect subsequent retries to transition from zero to non-zero, but is that guaranteed? Are there possibilities of deadlocks or race conditions? Can you go into some more detail (here or in the document) about how this works? Cheers, -Barry
On Oct 7, 2021, at 12:52, Sam Gross
I've been working on changes to CPython to allow it to run without the global interpreter lock. I'd like to share a working proof-of-concept that can run without the GIL. The proof-of-concept involves substantial changes to CPython internals, but relatively few changes to the C-API. It is compatible with many C extensions: extensions must be rebuilt, but usually require small or no modifications to source code. I've built compatible versions of packages from the scientific Python ecosystem, and they are installable through the bundled "pip".
Source code: https://github.com/colesbury/nogil
My goal with the proof-of-concept is to demonstrate that removing the GIL is feasible and worthwhile, and that the technical ideas of the project could serve as a basis of such an effort.
I'd like to start a discussion about these ideas and gauge the community's interest in this approach to removing the GIL.
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