[pypy-dev] Reference counting

[Maciej Fijalkowski]

On Sat, Jan 7, 2012 at 3:54 PM, Marko Tasic <mtasic85 at gmail.com> wrote:
> Maciej,
>
> Thank you for an express response.
>
>> Hi Marko, we're very glad to hear that!
>
> Off topic, but I have to mention that I've been an ambassador of PyPy
> for last few years.
> In beginning, it was hard, but now results that you've achieved are
> obvious and promising,
> and everyone starts to trust your implementation. However, I have to
> say that there
> are many notoriously xenophobic developers. Funny thing is that they
> trust how their
> source code is written but not how its executed.

Thanks :)

>
>> * refcounting is implemented as a transformation of flow graphs. See
>> pypy/rpython/memory/gctransform/refcounting.py for details. This
>> approach works very well in the sense we don't have to maintain
>> refcounts by hand in the interpreter (we'll never do that). This is
>> all well and good, however it also means there is a significant
>> redundancy in references. You would need to either implement a smarter
>> policy or a refcount-removing optimization (typically run after
>> inlining) in order for that to be viable.
>
> Is there a way to always have explicit reference counting field for all objects?
> I know this is bad, but I want to go even further. I would like to have even
> more fields in object structure besides refcount field. Reason for this is a
> way to test correctness of alternative RC implementations that handle cycles.
> I guess that I should turn off inlining?

What do you mean by explicit reference count? One that you manipulate
from the source of the Python interpreter? Then no. But if you mean
"can I have arbitrary fields on objects depending on the GC strategy"
then yes. The object layout is completely orthogonal to how the Python
interpreter is implemented.

>
>> * we generally never cared about avoiding cycles in the python
>> interpreter itself. I don't think pypy's refcounting implementation
>> comes with cycle detector included, but don't quote me on that
>
> I've developed an alternative way of handling cycles related to reference
> counting without using tracing GC, or traversing items in container objects
> such are list, dict, set, etc. Still checking algorithm and testing correctness,
> but everything has been fine until now. It is not my intention to make anything
> spectacular but just to research this field.
>
> If anyone has interest in my reference counting mechanism can check:
> http://code.google.com/p/cosmos-lang/wiki/CosmosRefCounter
> http://code.google.com/p/cosmos-lang/source/browse/doc/corc.py

People from unladen swallow tried to use the Cosmos GC or was it something else?

Again does that answer your questions?

PS. it sometimes easier to discuss such stuff on IRC than via mail.

Cheers,
fijal