On Fri, Apr 17, 2020 at 1:39 PM Victor Stinner <vstin...@python.org> wrote: > Sharing directly singletons like None can become a performance kill > once subinterpreters will run in parallel: > https://bugs.python.org/issue39511 > > Mark Shannon summarized: "Having two CPUs write to the same cache line > is a well known performance problem. There's nothing special about > CPython here. The proper name for it seems to be "cache line > ping-pong", but a search for "false sharing" might be more > informative." > > The problem is that PyObject.ob_refcnt should be protected by atomic > operations or locks if these objects are shared directly.
I agree. Sharing objects between subinterpreters is a recipe for pain. That's why the PEP says we will not. :) > I proposed to have singletons per interpreter, some people would > prefer immortal singletons. Yeah, we definitely have to sort that out before we make the GIL per-interpreter. > For bytes or buffer objects, I understand that you propose to share > the exact same PyObject objects between interpreters, at least in the > first implementation. > > It may be better to have one proxy object in each interpreter which > would control which interpreters can read and which interpreters can > write into the object. It's a similar but more complex issue than > singletons. It isn't the same Python object. It is the buffer that gets shared (for objects that support the buffer protocol). However, I suppose that it will have a similar problem to what you described above, since it is the same (read-only) memory in both interpreters. I'm not too worried about that at the moment though, particularly if we make the module provisional. -eric _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/FT6UOCKNOHAZVNNU6V5X6TYWCXFPWMWM/ Code of Conduct: http://python.org/psf/codeofconduct/
