[Python-Dev] GIL removal question

[David Beazley]

On Aug 10, 2011, at 6:15 AM, Nick Coghlan wrote:

> On Wed, Aug 10, 2011 at 9:09 PM, David Beazley <dave at dabeaz.com> wrote:
>> You're forgetting step 5.
>> 
>> 5. Put fine-grain locks around all reference counting operations (or rewrite all of Python's memory management and garbage collection from scratch).
> ...
>> After implementing the aforementioned step 5, you will find that the performance of everything, including the threaded code, will be quite a bit worse.  Frankly, this is probably the most significant obstacle to have any kind of GIL-less Python with reasonable performance.
> 
> PyPy would actually make a significantly better basis for this kind of
> experimentation, since they *don't* use reference counting for their
> memory management.
> 

That's an experiment that would pretty interesting.  I think the real question would boil down to what *else* do they have to lock to make everything work.   Reference counting is a huge bottleneck for CPython to be sure, but it's definitely not the only issue that has to be addressed in making a free-threaded Python.

Cheers,
Dave