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[Python-Dev] PEP 554 v3 (new interpreters module)

Antoine Pitrou solipsis at pitrou.net
Tue Oct 3 10:55:48 EDT 2017 
On Tue, 3 Oct 2017 08:36:55 -0600
Eric Snow <ericsnowcurrently at gmail.com> wrote:
> On Tue, Oct 3, 2017 at 5:00 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > On Mon, 2 Oct 2017 22:15:01 -0400
> > Eric Snow <ericsnowcurrently at gmail.com> wrote:  
> >>
> >> I'm still not convinced that sharing synchronization primitives is
> >> important enough to be worth including it in the PEP.  It can be added
> >> later, or via an extension module in the meantime.  To that end, I'll
> >> add a mechanism to the PEP for third-party types to indicate that they
> >> can be passed through channels.  Something like
> >> "obj.__channel_support__ = True".  
> >
> > How would that work?  If it's simply a matter of flipping a bit, why
> > don't we do it for all objects?  
> 
> The type would also have to be safe to share between interpreters. :)

But what does it mean to be safe to share, while the exact degree
and nature of the isolation between interpreters (and also their
concurrent execution) is unspecified?

I think we need a sharing protocol, not just a flag.  We also need to
think carefully about that protocol, so that it does not imply
unnecessary memory copies.  Therefore I think the protocol should be
something like the buffer protocol, that allows to acquire and release
a set of shared memory areas, but without imposing any semantics onto
those memory areas (each type implementing its own semantics).  And
there needs to be a dedicated reference counting for object shares, so
that the original object can be notified when all its shares have
vanished.

Regards

Antoine.
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